Thunder Mountain Lakes Blew My Mind

Note to the reader – this blog post describes a trip to fragile ecosystem via a risky trail. If you decide to follow me here, please use caution and turn up your leave-no-trace skills to 11. 🙂

The third time really is the charm. In June I tried to make it here but the road was still snowed in. In early July I started from a different lower-elevation trailhead, but the pass was…. still snowed in. The snow finally melted in early August – success!

I finally completed this truly magical backpacking trip.

I started from the Hope Lake Trailhead up Tunnel Creek Road off of Highway 2, just a few miles west of Steven’s pass. The Hope Lake trail heads uphill to connect with the Pacific Crest Trail, where I turned south. There’s a rockfall just south of Hope Lake that has a booming and adorable small mammal population – I saw 2 families of marmots and a family of pikas! After the steep first 2.5 miles of the hike the trail flattens out, the trees open up, and all of a sudden you expect Julie Andrews to pop out and start singing the Sound of Music.

The hike from here to Trap Lake is a delightful ramble through wildflower meadows and groves of pine trees.

I got to Trap Lake around noon, claimed a campsite, and made ramen for lunch. And then I started to climb. To get to Thunder Mountain Lakes you head up the PCT to Trap Pass, and then turn south onto a seriously sketchy trail that follows the county line south and up to Thunder Mountain Ridge. Sketchy as in if you slip, you fall 500 feet. Not for the faint of heart, and it could be risky for dogs.

The trail takes you up above the snow line, and starts to be marked with cairns to guide hikers through the snow field and bare granite. There are a few islands of vegetation, including stunted pine trees, pink heather, and blue dwarf lupine. The bees were going wild on the heather – I guess they only have a short window for foraging up here.

At this point I was 6.5 miles from the trailhead and 3,300 feet higher up in elevation. Just as I was having to start counting my paces to keep myself going, I turned a corner and my jaw dropped.

IMG_20200809_161907335_HDR

I had made it to Thunder Mountain Lakes! I could see all the way to Mt. Daniel and Hinman Glacier in the distance.

I hiked down to the lake and sprawled on the nice warm granite to eat a chocolate bar. As I got up to look down at the lower lake, I heard a rustle….

IMG_20200809_170640266_HDR

… and there was a mountain goat with her fuzzy baby! They’re such lucky creatures, getting to live here full-time. I hung out with them until they made their way along the ridge. The baby kept trying to sprint up onto rocks only to fall – luckily straight into its mom. It takes true love to be your offspring’s bouldering mat.

I lingered up by the lakes until the sun started to sink close to the ridgetop. The nice thing about hiking downhill is that it leaves me with more energy to spare to admire the rocks. The downside of admiring the rocks is that I get distracted and loose the trail. But these rocks were great!

They’re all granite, but conceal a subtle story. Textbook illustrations often depict magma bodies as single lumps that rise and cool neatly independently. Reality, as always, is more messy. Magma bodies (or batholiths, as they’re referred to once they cool down) in reality can merge, or pick up bits of other batholiths, or be reworked once they’ve cooled.

IMG_20200809_161220983

For example, this photo (above) shows a light gray batholith that cracked under pressure once it had cooled. A different kind of magma forced its way through the cracks as it rose, forming the dark grey stripe. Later the line of weakness was reopened and filled with hydrothermal quartz, creating the white streak. It’s kind of like a turducken of igneous rock.

IMG_20200809_181943594

And in this photo, the dark grey magma body ripped up chunks of a paler batholith as it rose and incorporated them into its mix, Pac Man style.

As I headed north back to Trap Pass I got phenomenal views of Glacier Peak as well as glimpses of Mt. Baker to the northwest.

IMG_20200809_174307847_HDR

Heading downhill back to my camp I met several fat marmots. Two of them were engaged in a clumsy but effective high-speed chase and high-volume screaming match. Their counterpart above Trap Lake obviously don’t think much of humans and screamed at me to let me know it. (lower left photo)

Trap lake was an idyllic place to spend the night, especially on a Sunday night when most of the weekend backpackers were long gone. I really got a prime campsite (above right) and enjoyed the luxurious packable chair that my sister (the one featured in all the Twin Trek posts on this blog) gave me for our birthday. Glamping all the way!

I spent a leisurely Monday in camp and then headed back to the trailhead at an equally leisurely pace. I really didn’t want to leave. Between snack, scenery, lunch, and pika -appreciation breaks I managed to stretch the 5 miles into 6.5 hours.

I may have had to drive back to civilization that day, but I’m definitely coming back here!

IMG_20200809_182920860_HDR

Rampart Ridge Rocks!

At Vanderbilt University’s Wilderness Skills club we classified adventure into two types of fun. Type 1 fun was fun to experience and fun to remember. Type 2, the slightly more common type, was miserable while it happened but either has a great reward or created a story that got you attention at parties.

The hike up to Rachel Lake after work with a 30-pound pack on my back was decidedly Type 2.

RampartRidgeZoom

Where in the world was I? Trailhead marked in blue, trail in dark green. map created in ArcMap by C. van Stolk using trail shapefiles created by the US Forest Service and ESRI’s Streets basemap.

Rampart Ridge trail map

Trail in bright green – map created in ArcMap by C. van Stolk using trail shapefiles created by the US Forest Service and ESRI’s terrain basemap.

I got off work early on that Friday, headed east on I-90, turned off at the exit for Kachess Lake, bounced up potholed gravel roads to the trailhead, and set out for adventure. I knew the hike went from 2,800 to 4,800 feet in four and a half miles. What I had foolishly overlooked is that it gains 1,400 feet in the last 1.2 miles. A significant distance of that 1.2 miles is literally in a creek bed. It had me questioning my life choices. I had planned to go all the way up to Rampart Lakes at 5,100 feet but I was absolutely done by the time I got to Rachel Lake. I was too cranky to eat my ramen noodles. I set up my tent at the outskirts of an inordinately crowded back country campground just as it got dark, made a cup of tea, and turned in for the night.

The next day was 100% heavenly Type 1 Fun.

I left the burden of my camping stuff where it lay and headed uphill into a clear blue day. My goal was Alta Peak at the northern end of Rampart Ridge, elevation 6,152 feet. I climbed up the ridge past fields of glacier lilies and heather and creeping phlox. It took me about two hours to make it to the top, with views of Mt. Rainier, Mt. Adams, and Glacier Peak. I settled in for an hour with my chair and my map to plan further adventures while I could see so much of the landscape!

IMG_20200718_103354040

Alta Peak, looking south at Mt. Rainier (center) and the Summit at Snoqualmie ski routes (center right).

IMG_20200718_094358509

Alta Peak, looking north (the white tip of Glacier Peak is peeking out from behind the Four Brothers on the center right)

IMG_20200718_111111261_HDR

Looking down past the snowdrifts to the basin below Alta Peak

I then rambled downhill to have lunch at Lila Lake. It was hopping with backpackers but I found a nice spot to eat my snack assortment and get yelled at by a marmot.

IMG_20200718_121029251_HDR

Once I had my fill of exploring the bouldery outcrops at Lila Lake, I headed south to Rampart Lakes. I spent the rest of the afternoon basking on a rock with a view at the Rampart Lake furthest along the trail. I braved the water for a swim and dried off in the sun while reading a mystery novel and enjoying my sippy flask of rosé. I did not join the hikers who were penguin-sliding down the snowdrift straight into the lake, though.

IMG_20200718_151253352_HDR

Rampart Lake, looking up at Rampart Ridge.

Around 6pm I headed back down to Rachel Lake to cook dinner and explore the campsite possibilities in the main campground for next time. I went to sleep in an exponentially better mood than I had the previous night.

Sunday morning I hoped to make it down the horribly steep creek bed part of the trail before the day hikers would be heading up it. Mission successful! I took loads of photos of wildflowers. I set up to finish my novel and eat lunch at a rocky waterfall overlook about a mile from the trailhead.

By this point Friday’s uphill slog was completely a thing of the past. All things considered, the trip had been a delight.

But wait! I couldn’t ignore the cool rocks. You know me.

The rocks exposed up at Rampart Ridge were gray with white clusters of larger elongated crystals. I thought they were really distinctive, but didn’t know their name.

It turns out these rocks have the epic moniker of “glomeroporphyritic basalt”. Glomeroporphyritic translates out of science Latin into “collected-together larger crystals”. In geology-ese, “porphyritic” refers to an igneous rock texture where larger crystals are set in a matrix of rock crystals with a much finer texture, like blueberries in a muffin.

Porphyritic igneous rocks form in two stages – the first one at deep in the earth’s crust, and the second in a shallower, cooler zone at or near the earth’s surface. The large white crystals in Rampart Ridge’s basalt formed when the magma was deep underground. They had plenty of time to slowly cool into large crystals in the hot environment at depth. However, some igneous or tectonic process suddenly shoved the magma body up towards the surface. This made the rest of the magma cool suddenly. Because these newer crystals did not have time to grow, they stayed very small.

But why did this one white mineral form crystals at depth, and not the others?  I turn to a familiar chart from my geology textbooks for the answer. It’s called Bowen’s Reaction Series, and describes the order in which minerals crystallize out of molten rock. This series springs from painstaking experiments involving pulverized minerals, a very very hot oven, and more patience than I possess. They revealed that minerals form into crystals at the different temperatures along a gradient.

The elemental mix of magma that becomes basalt creates the white mineral calcium plagioclase and the dark gray/black mineral pyroxene, with only trace amounts of other minerals. Calcium feldspar has a higher melting temperature, and so solidifies at a higher temperature while pyroxene has not yet formed into crystals. An important caveat is that not all magma contains all the elements necessary to make every rock in the series, so several minerals may be “skipped” in a certain magma body.

For example, quartz has the lowest melting temperature of all the common minerals, which is why it often forms decorative crystals or veins in the voids left when other minerals have already crystallized.

IMG_20200718_111029743_HDR

Quartz veins in volcanic rock higher up on Alta Peak.

The two kinds of rock I saw on this hike date mainly from the Eocene and Oligocene time periods between 55.8 and 23 million years ago. Washington was roughly at it’s current location on the globe back then and the volcanoes of the Cascades were starting to rev up. Since then, these rocks have been folded by tectonic forces, broken by faults, and eroded until they cropped out in the patchwork patterns that geologists map today.

rampart ridge edited map

Summarized in MS Paint from the original Snoqualmie Quadrangle Geologic Map by Tabor, Frizzell, Booth, and Waitt of the USGS: https://pubs.usgs.gov/imap/i2538/

The glomeroporphyritic basalt dates from the late Eocene period. It’s colored medium green and marked as Tnbg on the map above.

Tv and the light pink color stands for Oligocene volcanic rocks – an igneous jumble that’s a few million years younger than the glomeroporphyritic basalt. The rocks on Alta Peak are describe in the USGS pamphlet for the Snoqualmie quadrangle as “coarse volcanic breccia and tuff with minor ash flow tuff). They look almost like concrete made with blocky, angular aggregate. Breccia describes rocks created when magma shattered and engulfed surrounding rock as it erupted. Tuff forms when ash becomes cemented by its own heat, like how I described in the Smith Rocks post from 2018. Breccia makes up the ridgeline of the photo below – you can really see how this one rock classification encompasses a bunch of different kinds of rocks that erode differently to create a mix of straight ridge lines and messy talus slopes.

IMG_20200718_130156601

It’s hard to get a sense of the scale of the waterfall in the center from the photo. I could hear it roaring down the rocks from a quarter mile away!

I’m still doing research about how these rock types ended up juxtaposed. Western Washington’s rocks tell a complex story of bits of foreign continents (called accreted terranes) that were stuck onto the rest of North America by subducting plates, then covered with volcanic rocks and shuffled around by faults. It’s the northern relative to the process in Southern Oregon that I wrote about in my accreted terranes post. Up here, the terranes were even more altered by volcanism and faulting.

It definitely created a fantastic landscape!

IMG_20200718_104708892

Volcanic breccia on Alta Peak

Resources:

Definition of glomeroporphyritic basalt: https://blogs.agu.org/georneys/2011/07/14/geology-word-of-the-week-g-is-for-glomeroporphyritic/

USGS map and pamphlet for the Snoqualmie Quadrangle: https://pubs.usgs.gov/imap/i2538/

Info on volcanic breccia: https://en.wikipedia.org/wiki/Breccia#Volcanic

Information on Bowen’s reaction series: https://courses.lumenlearning.com/physicalgeology/chapter/3-3-crystallization-of-magma/

 

Ireland: Mining’s legacy in Glendalough

After Heather and I explored Brittany we headed north to join 35 other van Stolks and their partners in Ireland for a family reunion. No, we aren’t Irish, but the Dutch family wanted to vacation outside of the Netherlands and the American part of the family wanted to spend time in a scenic part of northern Europe. Ireland was a delightful compromise. We converged on a holiday cottage complex just north of Dublin where we spent a convivial time moving from porch to porch catching up on years of news. The whole bunch of us set out in a rather unruly convoy to highlights like Newgrange, Slane Castle, and a sheep herding demonstration further afield in Glendalough.

Ireland trip

Glendalough is a jewel of a lake in the mountains south of Dublin in County Wicklow, a rugged contrast to the gently rolling green hills usually associated with Ireland. We all oohed and aahed at the sheepdogs and their  puppies, and then a smaller group of cousins set out on a hike to work off the cabin fever.We did the “white trail” around the upper and lower lakes at Glendalough. It’s a stunning 7.8 mile loop! We did it counter-clockwise, which results in a gentler upward climb. If you hike this clockwise you have to climb up the hundreds of wooden stairs on the eastern side of the lake… not my idea of a great time. Going counter-clockwise also results in beautiful views of the monastery site from the top of the cliff!

Glendalough white trail

Trail map from Alltrails.com

It turned out to be a lesson in the importance of looking at the scale of the contour lines on the topographic map at the visitor’s center. We thought “oh, we only cross one topo line on the map, the trail must stay close to the lake.” Well it turned out that the distance between topo lines on that map was 0.4 kilometers – about 1,500 feet. My cousins with a strong aversion to heights were absolute troopers. The views from the top were amazing!

IMG_20190731_154713964_HDR

Hanging out in a textbook-perfect glacial valley, with the old mine buildings in the background. Halfway to the top!

IMG_20190731_172711925_HDR

At the top! Two cousins aren’t in this picture because they didn’t fancy spending more time at the top of this cliff than absolutely necessary and they also are much fitter than the rest of us.

IMG_20190731_171351115_HDR

The southern cliff is topped with blanket bogs. They’re an extremely soggy and sensitive landscape, so the park put in a couple miles of boardwalk to minimize human impact. I felt like I was somewhere in Tolkien’s Middle Earth!

Glendalough seems like a valley outside time, once you step away from the tourist shops. The paths take you by an old monastery, streams in strange mossy landscapes, and the lake itself surround by hills and forests. It came as a surprise to me when we found the remnants of an abandoned mine at the eastern end of the lake.

IMG_20190731_155611054

It turns out that between the 1790s and the 1920s this area a hive of mining activity. You can easily tell what the miners were looking for in the landscape – the scars of white quartz rubble are the giveaway (see the slope on the right side of the photo above). The miners were looking for lead, silver, and zinc. Specifically, they found it in the minerals galena and sphalerite.

Image of galena (dark gray) and sphalerite (orange-ish brown) in quartz (white) from the Glendalough mine from the National Museum of Ireland.

Galena is a mineral composed of equal amounts of lead and sulphur (its formula is PbS). In this area silver substitutes for lead in the crystal structure around 5% of the time, making it a valuable ore for silver as well as lead. Sphalerite is made of equal amounts of zinc and sulphur (formula is ZnS). But how did they get here, and why are they only found in the quartz?

Let’s take a step back an look at the history of the local landscape over the past few million years, courtesy of an interpretive sign at Glendalough’s ranger center. The information is great so I didn’t bother re-typing it, but you may have to click on the image and zoom to read it if you’re reading this on your phone.

 

Photo of an interpretive sign of Glendalough's geology at the ranger center.

Photo of an interpretive sign of Glendalough’s geology at the ranger center.

Two types of rocks form the foundation of this landscape: a metamorphosed version of mudstone or shale called schist, and the granite which muscled its way up into those rocks during the Caledonian orogeny. Remember that from a few blog posts back? This Irish granite is a cousin of sorts to the granite that became the Mont Saint Michel. It too was formed as the heat created by the collision of Laurentia, Baltica, and Avalonia created magma that rose up into overlying rocks and cooled into huge lumps of granite (called batholiths in geologist jargon). In the map below, the granite is shown in red. It also shows just how many mines were once active in this area!

Glendalough mining

A map of mining activities near Glendalough – we hiked past #7 and #8, Glendalough Valley mine and Van Diemen’s land mine. This map also shows the geologic contrast in the region between the schist (light pink) to the east and the granite (red) to the west of the lake. This map is from https://secure.dccae.gov.ie/GSI_DOWNLOAD/Geoheritage/Reports/WW065_Glendalough_Glendasan_Glenmalure_District_Overview.pdf

This particular batholith is called the Leinster Granite batholith and underlies much of County Wicklow. It’s harder than the surrounding schist and creates more rugged cliffs when assaulted with millions of years of wind, rain, and glaciers. In the Wicklow mountains the granite slopes tend to be covered in boulder fields, and the schist slopes are covered in heather and other creeping low bushes. Neither type of rock weathers into particularly inviting soil for plants, at least not in the geologically short period since the last Ice Age.

img_20200329_152846214_hdr
Rock specimens that I couldn’t resist at Glendalough: Schist with neat protruding flexible sheet of mica (left), granite (center), bits of waste quartz from the mining operation (right)

Here’s a map of the mine site that is #7 on the map above, and the first area we came to on our hike. This map was put together by the educational group “Glens of Lead”. This group put up some great historical signs in along the park about how the old mining operations worked.

20140911084002_glendalough_mines_walking_map_preview_0

And here’s a map of the second area on the hike, #8 on the map.

20140911085513_Van_Diemens_Land_Mine_walking_map_preview_0

Very little of the original infrastructure remains today, except for the stone buildings at the Glendalough mine site and the bright white quartz of the tailings rubble from the mines. The shafts and tunnels have been blocked off and the old tramways completely dismantled. The site seems very wild again.

IMG_20190731_171519154

Standing on the schist side of the valley, looking over to the steep granite cliffs and the piles of quartz tailings below the exits of the old mine shafts 1,000 feet below.

Above right: granite with vein of hydrothermal mineralization (foot for scale) in the mining area, compared with schist exposed at the top of the cliff on the south side of the lake.

But how does lead ore get into quartz veins? I’ve written about continental collisions and granite before in this blog, but not really about smaller processes of metamorphism. It’s time to fire up MS Paint again.

subduction

Magma bodies (red) rise off of the subducting oceanic crust and cool into intrusive igneous rocks (pink). Water (blue speckles) in the oceanic crust allows the crust to melt at lower temperatures than the surrounding rock, and travels upwards as a part of the magma. Diagram by C. van Stolk.

Back around 300 million years ago, the ocean Iapetus was closing as the old continents Laurentia, Gondwana, and Avalonia moved towards each other. The oceanic crust under Iapetus had to go somewhere; it subducted under the continents. After a few million years of being underwater that oceanic crust was pretty soggy as rocks go. The conveyor belt of plate tectonics drove the heavy oceanic crust down under the lighter continental crust.  It began to melt as it sank beneath the continent and into the upper layer of Earth’s mantle called the asthenosphere.

It turns out that this water trapped in the crust is kind of the “secret sauce” of metamorphism. The presence of water allows rocks to melt at lower temperatures than they would otherwise. Metamorphism boils down to two variables – heat and pressure. Both increase vertically with depth in the earth’s crust. Pressure also increases horizontally in collision zones. In the presence of equal amounts of heat and pressure, wet rock will melt to a greater degree than dry rock.

Anyone who has taken a ride in a hot air balloon learns that heat rises – the hot air in the balloon keeps the passengers aloft in the cooler surrounding air. The blobs of magma rising from the subducting wet oceanic crust are much like extremely dense, slow-motion hot air balloons – they rise through any weakness they can find in the surrounding cooler and drier rock. The blobs of magma become batholiths of intrusive rock when they cool, like the granite here. As the granite cooled, the heat had to go somewhere, just as the oceanic plate had to go somewhere as the ocean closed. The magma “cooked” the shales that surrounded it into the metamorphosed version – schist (see purple “contact metamorphism” on the diagram below). However the story of the water that magma contained isn’t over.

subduction with contact metamorphism

If water can’t fit into the crystal structure of the magma as it cools into intrusive igneous rocks, it is released from the melt. It takes along ions that can be dissolved in it and travels into cracks in the surrounding rock. Often these “cracks” are caused by faults or by joints caused by horizontal pressure. One of the most common elements carried along this way is silica, which in combination with oxygen forms quartz veins as it cools. This mineral-rich hot water is called a “hydrothermal solution”.

Image with no description

Diagram of hydrothermal alteration from https://opentextbc.ca/geology. (a) Shows a magma body that has risen into cooler rock and is “cooking” it shown by the purple aureole. (b) Shows magmatic water being released from the magma body through veins. (c) Shows how groundwater moving past the magma body can also carry dissolved minerals away from it to other locations.

As the hydrothermal solution rises and cools, minerals form out of the solution like rock sugar forming out of hot sugar syrup as it cools down. Not every part of the solution is really well mixed – some parts of the solution are like oil and water and stay somewhat distinct as they travel together. Examples of this are silicate minerals (i.e. quartz SiO2, feldspar KAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8) and sulphide minerals (galena PbS, sphalerite ZnS). As the solution cools, these two types of minerals form adjacent but separate structures.

So here at Glendalough, you have granite and schist cut through with veins of hydrothermal rocks that contain chunks of sulphide ore minerals in the more abundant quartz. The miners followed these hydrothermal veins to find the valuable ore, and discarded the attractive but comparably worthless quartz in tailings piles at the site after the rock was put through a huge crusher to break out the softer sulphide ore minerals. I was sorry to notice that they were so thorough that a casual geologist really can’t find any of that ore nowadays.

I was happy enough to take away great memories, beautiful views, and a few new rocks in my pocket.

Resources:

A good brief history of the mines here: https://www.mindat.org/article.php/368/A+History+of+Glendalough

Brief intro to geology of Glendalough here: https://www.wicklowmountainsnationalpark.ie/nature/geology/

https://www.gsi.ie/en-ie/geoscience-topics/geology/Pages/Geology-of-Ireland.aspx

detailed geological survey of mining in the region: https://secure.dccae.gov.ie/GSI_DOWNLOAD/Geoheritage/Reports/WW065_Glendalough_Glendasan_Glenmalure_District_Overview.pdf

detailed geological survey of mining at Glendalough specifically: https://secure.dccae.gov.ie/GSI_DOWNLOAD/Geoheritage/Reports/WW025_Glendalough.pdf

geological map of Ireland: https://secure.dccae.gov.ie/GSI_DOWNLOAD/Bedrock/Other/GSI_BedrockGeologyOfIreland_A4.pdf

Maps of lead mining in the area by the local education group “Glens of Lead”: https://www.avenzamaps.com/vendor/209/glens-of-lead

More about the Iapetus Suture, which connects the half of Ireland/Scotland that was once Laurentia (proto-North America) with the half that was once Avalonia (proto-Europe). https://en.wikipedia.org/wiki/Iapetus_Suture

Interesting map of the terranes that make up Ireland: http://www.askaboutireland.ie/reading-room/environment-geography/physical-landscape/Irelands-physical-landsca/the-formation-of-the-phys/

Ireland through geologic time: https://www.gsi.ie/en-ie/education/the-geology-of-ireland/Pages/Ireland-through-geological-time.aspx

Specimen of galena in quartz from the mine: https://www.museum.ie/The-Collections/Documentation-Discoveries/July-2016-(1)/Lead-Bearing-Minerals-from-Glendalough

More about contact metamorphism/hydrothermal alteration/sulfide ore bodies

Contact metamorphism with good diagrams: https://opentextbc.ca/geology/chapter/7-5-contact-metamorphism-and-hydrothermal-processes/

http://www.geologyin.com/2014/11/veins-and-hydrothermal-deposits.html

Overview of sulfide ores: https://uwaterloo.ca/earth-sciences-museum/resources/hydrothermal-minerals

Cliffsnotes version of hydrothermal metamorphism: https://www.cliffsnotes.com/study-guides/geology/metamorphic-rocks/hydrothermal-rocks

Detailed review of ore genesis, including immiscible solutions. https://courses.lumenlearning.com/wmopen-geology/chapter/outcome-ore-and-mineral-resources/

Crazy pink rock formations at the Cote du Granit Rose

Part 2 of the geology of my summer vacation. For an idea of where this fit in our trip, check out the travelogue post. This post follows the first post on Mont Saint-Michel.

I had left all of the vacation planning in Heather’s able hands so I could focus on my thesis last spring. My only requirement (only halfway in jest) was that the vacation had to include eating pastries on rocks. And boy, did Heather deliver! Days 5 and 6 of the trip found us near Trebeurden and Ploumanac’h on the fabulous pink granite coast. The sun was shining, the pain au chocolat was as delicious as I had ever hoped for, and a giant granite playground awaited us.

croissant and rocks

my dreams came true!

There isn’t a shortage of granite on the Brittany coast – we met some in the last blog post too. Much of was grey and only visible in isolated outcrops. As we hiked east from the little port of Ploumanac’h along the coast, the grey granite gave way to crazy piles of unmistakably pink rock! I couldn’t help but start wondering what caused the change in color, not to mention the weird shapes!

It turns out that the explanations come in threes: the pink granite is made of three minerals, it belongs to one of three different igneous events in the region, and three different substances have sculpted the granite into the wild shapes at Ploumanac’h.

The pink granite gets its rosy hue from potassium feldspar, while the greyer granite has more creamy-colored plagioclase feldspar in its makeup. I illustrated their mineral composition in the figure below. The natural history museum in Ploumanac’h informed me that the pink granite is  approximately 50% potassium feldspar, 30% quartz, and 20% biotite. They didn’t give details about the less glamorous grey granite and I was too focused on getting to the pink stuff to even take a close-up of it, so I’ve only approximated its composition.

Pink Grey Granite Comparison

Both colors of granite at Ploumanac’h were put in place around 300 million years ago (mya) during the last gasps of a mountain-building event as the ancient continents of Gondwana and Laurussia crashed together to form Pangaea. I talked in depth about this massive game of continental bumper-cars in the previous post, so I’ll skip it here. Over time erosion unearthed the buried masses of granite, as shown in the figure below.

pink granite emplacement diagram.png

Photo of a diagram in the exhibit at the Maison du littoral, text translated by me.

To get even more specific, the granite in the area was put in place in three physically distinct phases around 300 mya. In the first phase, two magmas with different compositions intruded the surrounding metamorphic rock at the same time. The first was rich in silicon and formed the coarse-grained pink granite and the second was poor in silicon and formed the dark gabbro visible near Tregastel. These two igneous rock types melted in the same event from two different types of source rocks, giving them their unique compositions.

During the second phase, another silica-rich magma forced its way into joints in the now-cool first pink granite. This magma had a similar composition  to the pink granite in the first event but cooled more quickly than its predecessor, forming smaller mineral crystals.

In the third phase, a magma with a more basic (as in pH) composition intruded into an dome-shaped weakness in the cooled granite from the first two phases. This magma cooled into the blue-gray granite near Ile-Grande.

The difference between the colors of the ~520 million year old granite at Mont Saint-Michel, the ~300 million year old grey granite at Trebeurden, and the ~300 million year old granite at Ploumanac’h isn’t merely ornamental. The rocks’ mineral compositions give geologists clues to the kinds of source rocks that melted into the granite. Feldspars and quartz have high silicon:oxygen ratios in their composition, and so indicate that abundant silica was present in the source rocks.

A whole host of different kinds of minerals are built from silica and oxygen, ranging from the densest minerals with 4 oxygen atoms  for every 1 silicon atom to the less dense minerals with only 2 oxygen atoms for every 1 silicon atom. In general, the less dense silicon-rich minerals are more represented in the continental crust, while the denser silicon-poor minerals are more common in the oceanic crust.

You can see these relationships between minerals’ properties and igneous rock types below in the igneous rock classification chart every mineralogy student learns by heart by the end of the term. It’s only a guideline – if a mineral was missing from the source rock, it will not show up in the igneous rock created from its melting. For example, amphibole and muscovite are missing from the pink granite.

This indicates that the pink granite was formed predominantly by the melting of low-density, high-silica rocks at low melting temperatures. The grey granite at Trebeurden is a little bit to the right of the pink granite on the classification chart – still a granite, but including more minerals with higher melting points and less potassium feldspar (a.k.a.  orthoclase feldspar). The gabbro at St. Anne is even further to the right, and likely formed from the melting of a chunk of oceanic crust. Sometimes rocks are completely off this chart. For example the magma that formed the pale granite that we saw at Mont Saint-Michel either melted at low temperatures (geologically speaking) of ~600 C or melted from source rock whose chemistry didn’t allow for the formation of dark mica or amphibole crystals.

So I figured out why the granite was pink instead of grey. But what created its otherworldly shapes? And where did all these boulders come from?

Usually boulders are created in steep landscapes where chunks of rock falling off the canyon walls are tumbled aggressively in mountain streams and carried long distances. In contrast, these boulders have barely moved relative to each other since the granite cooled! They were formed in place by erosion, shown in the diagram below. The technical French term for this formation is “un chaos”, which seems very appropriate.

granite chaos creation

The important factor here is a change in the rate of weathering and erosion. In this case, the erosion regime changed from slow dissolution of the rock by groundwater (shaping the granite into boulders underground) to more rapid erosion as the waves crash on the shore (exposing the boulders).

Once the boulders are exposed to the elements, two slower types of chemical erosion nibble them into even more convoluted shapes. Chemical reactions between salt spray and the the mica and feldspar crystals in the rock transform them into weaker clay minerals that wash away, creating divots and creases in the rock wherever salt collects.

As saltwater works on the rocks from the top, organic acids in soil eat away at the rocks at ground level over tens of thousands of years to create subtle mushroom shapes.

acidic soil erosion

The end result is an utter delight to explore!

IMG_20190717_111226870_HDR

Heather points out a quartz vein in the pink granite. The boulder on the center left shows a distinct salt weathering divot on its top.

pink granite castle

Climbing to the top of a formation, I found a 2-foot deep crenelated “crow’s nest” formed by salt weathering!

Sources (all are in French):

Great summary from the local natural history museum, the Maison du littoral: http://ville.perros-guirec.com/fileadmin/user_upload/mediatheque/Ville/Maison_du_littoral/refonte_page_environnement/expo_origine_du_granit_roseBD.pdf

Less technical summary from the local tourist board: http://www.cotedegranitrose.net/la-cote-de-granit-rose/geologie-le-granit-rose/

Long and extremely thorough field trip guide published by the Geological and Mineralogical Society of Brittany: https://sgmb.univ-rennes1.fr/geotopes/decouvertes/23-decouvertes/67-ploumanac-h

Short summary/technical field trip guide: http://www.saga-geol.asso.fr/Geologie_page_conf_Ploumanach.html

 

Twin Trek 2019: France!

This is a “travelogue” post – more geology specific posts to follow!

My sister and I had a fantastic opportunity for out annual “Twin Trek” this year! My family was having a reunion in Ireland, so our transatlantic plane tickets were covered… it opened up a whole new continent of possibilities. I handed all the responsibility for choosing a destination over to Heather, pleading that I didn’t need such a tempting distraction while finishing my thesis. I told her that as long as I could eat pastries while sitting on rocks at some point I would be happy. She’s a gem and put together a fantastic itinerary in France! Both of us had studied abroad in the south of France in college, and she had spent a year teaching English in Normandy. This time, she decided that we would explore a beautiful region that she had briefly visited and wanted to return to – Brittany, in the northwest. We hostel-hopped from Rennes to Mont-Saint-Michel to St. Malo to the Pink Granite Coast to Finisterre, then back to Rennes and on to Paris. Being over 25 and being able to get a rental car felt so luxurious… the last time we were in France as college students we got an education in foreign public transit out of necessity.  I created an ArcGIS Online map of our route and have included a link to it below (unfortunately, free WordPress accounts can’t embed maps). I love the new watercolor base map that is available! The link is followed by screenshots.

(You can reach the map of our trip location directly at this link)

twin trek map zoomtwin trek map zoomed out

I’m looking forward to writing several posts about this trip. I’m sure the research will stretch my command of the French language in new directions, but it will be a fun scavenger hunt to see what information I can find!

  1. What geologic features allow Mont-Saint-Michel to rise above the tidal flats?
  2. Why is the granite in Ploumanac’h and the rest of the “Cote de Granit Rose” so pink?
  3. When created the spectacular white cliffs near Camaret-sur-Mer on the Presque-Isle de Crozon?
  4. Why are there so many sea caves near Morgat, also on the Presque-Isel de Crozon?

But in this post, I’ll just share the travel diary part of the story.

I was cranky, jet lagged, and hadn’t slept in 20 hours when Heather picked me up from the train station in Le Mans. I’m not sure which one of us was more frazzled – she had spent the previous few hours reintroducing herself to driving stick shift in a tiny car on tiny roads after six years driving exclusively an automatic. So as glad as we were to see each other it was a very quiet car ride to Rennes, where we checked into the hostel and went in search of Brittany’s specialty: buckwheat crepes filled with delicious things. We felt significantly better about the state of the world when our food arrived, accompanied by traditional Breton teacups of hard cider.

Rennes was a wonderful place to recover from jet lag and feel like I was truly in France. Brightly painted timber-and-plaster houses lean crookedly against each other like they’ve had too many teacups of cider and surround gothic-style churches and squares full of cafe tables. After getting lunch (crepe-wrapped sausages) at the huge Saturday market at the Place des Lices, Heather and I wandered through the shopping district to the Jardin de Thabor. Once a monastery garden, the public gardens got a scenic 19th century renovation to include paths, grottoes, a botanic garden, and a delightfully random aviary. The lawns were packed with people escaping un-airconditioned apartments to catch breezes in the shade. We parked ourselves on a shady bench by the rose garden to finish the rest of the basket of strawberries. By that time my internal clock was in revolt. I went back to the hostel to crash until Heather lured me out of the room with promises of  new kinds of crepes and a glass of rose.

The next day we set out on the Twin Trek in earnest. Heather was excited to finally see Mont-Saint-Michel in sunny weather, and I was curious as to whether it would equal the hype. It turned out that getting there early on a Sunday was a great decision – the tour buses from Paris must have been running late because there were pleasantly few other tourists there. We could really imagine that we had stepped back in time. The stories on the audioguide of the Abbey made the small fee well worth the money. There aren’t many interpretive signs to bring the impressive but stark walls of the abbey to life; the audioguide explains not only the construction of the abbey but the history that it witnessed and the lives of the religious orders that lived there. We had lunch on the ramparts beside a family of seagulls who watched us with great interest and eventual disappointment when we refused to share.

Heather and I headed back to the car once tour groups started to flood the island in earnest – the small streets were so crowded that we had trouble elbowing our way back down to the gate. We drove to the storied port town (and pirate hideout) of St. Malo, settled into the hostel, and walked down the beach’s boardwalk to find a crepe place in the historic walled city. It’s amazing – the city was 75% destroyed during WWII, but was painstakingly rebuilt stone by stone so it looks unchanged since the 1600s! We missed the last bus back to the hostel and stayed to watch the Bastille Day fireworks. The fact that the sun set at 11 pm was really throwing me off!  Especially because we had big plans for the next day – a hike from St. Malo to Port Mer along the coast.

We took the number 8 bus to the Ilots stop, and then hiked the GR (Grand Randonee) 34 to Port Mer where we caught the bus back to the hostel. We weren’t using a map, but it turns out that it was over 11 miles. It was a hot, sunny day and the coast was beautiful – all sheer cliffs, ruined castles, and sailboats tacking between tiny islands. Also, as it turned out, nude beaches. So despite the ocean views, there were some parts of the route where we chose to admire the landward side of the trail. I’ve included an interactive web map below. Although it may look like we walked on water, those parts of the route actually indicate tidal flats. There’s such a huge tidal range here! When we left at the morning the sea was a between 1/2 mile and 1/4 of a mile away from the boats stranded on the tide flats, and in the evening the boats were floating. Heather and I agree that we would recommend taking the bus one stop further to La Guimorais to get straight to the prettier parts of the hike.

(You can link directly to the interactive map here)
st malo port mer map
After a well-earned dinner and beers at Port-Mer, we took the bus back to St. Malo and slept very well that night. If you weren’t doing this hike in the summer, you’d have to go all the way to Cancale to catch a bus back to St. Malo – the bust line that serves the beaches is seasonal.

After a morning exploring the ramparts of St-Malo and hunting down ermine-themed souvenirs, we started the drive west to our next hostel in Trebeurden on the Cote de Granit Rose. Once we reached the hostel, I switched into the driver’s seat and Heather navigated us to the surreal-looking geologic destination that she had been promising me – the pink granite near Ploumanac’h. We had a leisurely happy hour, hike, and dinner while watching the sun slowly set over the Channel.

IMG_20190716_203311950_HDR

We met more opportunistic seagulls while eating our picnic dinner on the pink granite

IMG_20190716_212605162_HDR

Heather hanging out with a “chaos” of pink granite boulders in the background. The boulder had been sculpted into crazy shapes by water and wind!

The next morning, I dragged Heather out of bed bright and early so that we could go back to the geologic museum I had seen at the Maison Littorale along our hike the previous evening. It gave me plenty of material for a future blog post on the granite we were scrambling over, and the Heather bought me a lovely small piece of polished local granite from the gift shop as a birthday present. She knows me well, and yes I am literally that person who fills their suitcase with rocks. In my defense, it wasn’t much bigger that a bar of soap. The museum also had an exhibit on how the park was trying to restore vegetation, so Heather and I tried to be good stewards when we were using the boulders as adult-sized jungle gyms. There were still plenty of rocks and tide pools that we could get to appropriately! The tide pools here look different than the ones in Oregon – the coralline algae is grey instead of pink, and the predominant anemones are smooth, dark, and glossy instead of rough and green.

It was hard to drag ourselves away from that amazing coastline, but we also know we needed to make it to our next stop that night. We had lunch with the chickens at the hostel, loaded up the car, and drove a two hours to the small fishing port Cameret-sur-Mer on the Presque-Isle de Crozon. We went on a hike before dinner with a plan to explore a surrealist poet’s ruined mansion, and menhir alignment, and the Point de Pen Hir. Along the way, we stumbled across a huge complex of WWII bunkers and sobering memorials to the 638 French merchant marine ships and many Bretons lost in the war.

The next day dawned grey and cloudy, and Heather had planned for us to hike near Kerloc’h and then rent kayaks. That original plan was foiled when the boat rental shop told us that the westerly wind was too strong to rent kayaks from Kerloc’h, and so we went to Morgat on the opposite side of the Cape de Chevre where the wind was more favorable.The day was still cloudy and cool when we hauled our kayaks to the edge of the tide flats. That rental staff looked at us like we were crazy and suggested renting wetsuits, but the sun came out a few minutes after we launched! It turned into an absolutely perfect day to be on the water. The wind was still unpredictable though – one sneaker wave tossed Heather and her kayak into a complete somersault as she was pushing off from a beach, scraping up her arm and scattering her belongings across the waterline. She maintains that it was OK because getting a scar at sea ought to make her an honorary Breton pirate.

Relocating our kayak adventure to Morgat had a major unexpected silver lining: sea caves!! The coastline was steep, convoluted, and carved into fantastic arches and caverns. When the tide is high you can paddle into some of them…although the incoming tide created significant whitewater in some of them. Heather and I had a blast surfing the waves in the more exciting caves but it may not have been the smartest thing to do. When a family with small kids on the bows of their kayaks asked us where the “Devil’s Chimneys” were, we crossed our fingers behind our backs and feigned ignorance.

Th next day, the clouds of the previous day turned into genuine Breton downpours. We gave up the idea of outdoor adventures in favor of taking a bouncy ferry ride across the inlet to the huge port of Brest. Unlike Rennes, it doesn’t have that old-world scenic French flavor. It was bombed completely flat during WWII and hastily rebuilt in cubic concrete except miraculously for one thing – the ancient fort. It now houses the French naval offices and also a great maritime museum. I wish I could have teleported my dad there to enjoy the exhibit on around-the-world racing in catamarans for the Jules Verne Trophy.

The next day was pretty tame… we poked around the many art galleries in Camaret-sur-Mer, and then drove back to Rennes. The following morning we took the train to Paris to meet up with Heather’s girlfriend Elaine.

While it was relatively warm in Brittany, the “canicule” (poetic French term for heat wave) was merciless in Paris during the five days of our stay. A change from the usual atmospheric patterns caused more hot air than usual to push its way north from the Sahara into countries much worse prepared to deal with it. The daily high temperature ranged from 97 to 108 degrees F , while the average high for July is 78. This forced us to change our usual travel patterns and take a more relaxed approach to Paris than we had planned. We made it through the week with strategic applications of siestas, Orangina, and ice cream.

Over the course of the visit the three of us visited the Pantheon (mercifully cool, and with a fascinating exhibit on deaf history), the Musee d’Orsay (packed, but worthwhile for the amazing exhibit on Berthe Morisot), Sacre Coeur (overrun by tourists diverted from the closed Cathedral de Notre Dame, and quieter directly after services), Musee de Montmatre (an quiet oasis well worth the admission cost with delightful exhibits about impressionists and the neighborhood), and the Catacombs (Elaine’s favorite for the Spooky Aesthetic ™, and a standout for me for the ancient history of mining). I’ll definitely write another post about the elaborate system of mines and tombs under Paris!

On the last day of our stay, we successfully navigated a packed metro with our luggage, Heather led the way to the most well-hidden municipal bus depot I’ve ever encountered, and we headed north to meet my parents and visit my grandmother in Belgium. Thank heavens the bus was air-conditioned.

IMG_20190716_201914470

Can’t I just teleport back to Ploumanac’h?

Next up: geology posts.

After that: Ireland!

Sisters visit South Sister (and Green Lakes)

This post covers Day 2 of the Annual Twin Camping Trip: for Day 1 check out Smith Rock Hike: Volcanic Rocks, Volcanic Heat.

twin trip locations

Heather and I woke up bright and early on a chilly morning to get a head start on the popular Green Lakes trail up to the base of South Sister, one of a trio of snow-capped volcanic peaks west of Bend. We hiked Trail 1.7 (traced in yellow on the map below), and stopped for lunch at a very scenic overlook (red dot). Including all our side jaunts, it was a 11 mile round-trip hike with about 1,000 feet of elevation gain from the trailhead to the lakes. We were three thousand feet higher here than at Smith Rock, so thankfully it was much cooler.

twin-hike-map.png

Fall Creek is aptly named – and it’s absolutely beautiful!

 

 

Just when the ponderosa pines and waterfalls are starting to become routine, the view opens up onto the jagged slopes of the Newberry rhyolitic dome from South Sister’s most recent eruption 2,000 years ago. Although it looks inhospitable it actually is a perfect home for a variety of adorable rodents. A little pika and several yellow-bellied marmots stuck their noses out of the rubble to say hello. Too far away to photograph, alas, you’ll just have to take our word for it. Heather said that the lava flow looked like Mordor from the Lord of the Rings… maybe a lair for the ASBOG Balrog?

IMG_20180806_095746544_HDR

Related image

Pika, photo from the National Wildlife Federation

Marmota flaviventris (Yellow Bellied Marmot), Yosemite NP - Diliff.jpg

Marmot, photo from Wikipedia

These lava flows blocked the Fall Creek drainage thoroughly enough that debris and water built up behind them, creating the spectacular Green Lakes!

IMG_20180806_104013383

Almost there…

IMG_20180806_105816520

The very top of North Sister peeked up above the flanks of South and Middle Sister in this shot

IMG_20180806_123722077

Heather contemplates how much work it would take to bring a kayak up here…

As we sat to eat lunch at the overlook we were entertained by the profanity yelled by hikers who decided to gleefully jump into Green Lake only to discover how freezing cold it is, even in August. Let’s just say that when I stuck my feet in the lake to cool off it only took about 10 seconds for them to go numb… I’m not tempted to turn that into a full-body experience.

IMG_20180806_125729322

Ultimate Sisters selfie: Heather, South Sister, and me

We were pretty beat by the time we descended back to the trailhead and happily fell into our hammocks with libations back at Elk Lake. It was another hour or two before we felt like moving again, and we made dinner with the last bits of daylight. Afterwards we took advantage of the clear skies to stargaze – Heather had never seen the Milky Way except in photos. Stupid southeast/east coast light pollution. I’m so glad we could fix that – we had an amazing view not only of our galaxy but of several shooting stars that put on a show! The next morning we packed up camp and headed out on the next adventure to an even bigger volcano: Crater Lake National Park.

But before we leave the Sisters… what were we hiking on?

All three Sisters are part of the High Cascades, the range of distinctive volcanoes in Oregon and Washington that formed between approximately 35 million years ago and the present. I gave a bit of a teaser to their history in my post about Dome Rock in the Western Cascades – I could see the Sisters from there.

Three Sisters annotated photograph viewed from south to North from Broken Top, Oregon.  (Click image to view full size.)

Three Sisters Family Portrait, from their USGS Volcanic Hazards website

The Sisters, while linked together by their names, are not triplets. North Sister is by far the eldest; it was formed between 120,000 to 45,000 years ago by basalt and andesite lavas and eruptions. Middle Sister formed between 40 and 14 thousand years ago, but primarily between 25 and 18 thousand years ago, putting it close in age with South Sister. It is built of andesite, dacite, and rhyolite, and is famous for the archaeologically significant Obsidian Cliffs formed in one of its eruptions that became a tool-making bonanza for Native Americans.

Here’s more specific timeline that I drew for South Sister, based on information from the US Geological Survey Volcanic Hazards Program (USGS VHP).

South Sister eruptive history

You can get an idea of the wide range of eruption ages in the figure below from the Oregon Department of Geology and Mineral Industries (DOGAMI)’s recreation brochure for the area.

DOGAMI eruptive history figure

twin hike map with lava flows

Clip from the DOGAMI recreation map that I edited to show the most recent South Sister Flows from 2,200 to 2,000 years ago: the “Devil’s Chain” flows are in purple while Rock Mesa is outlined in Green. There are so many “Devil’s Whatcha-ma-callit” features in Oregon, some cartographers must have had a flair for the dramatic.

While South Sister hasn’t erupted in two thousand years and the Middle and North Sisters have been dormant even longer, the USGS isn’t ruling out future eruptions.

“The Three Sisters region has hosted volcanic eruptions for hundreds of thousands of years, and future eruptions are a certainty. Two types of volcanoes exist in the region and each poses different hazards. South and Middle Sister are recurrently active over thousands to tens of thousands of years and may either erupt explosively or produce substantial lava domes that could collapse into pyroclastic flows. They could also produce lava flows. In contrast, less explosive eruptions could occur almost anywhere in the surrounding area, and construct small cinder cones to large shield volcanoes made mostly of basalt to andesite lava flows. These volcanoes are typically short-lived (months to centuries) and usually don’t erupt again”

If it’s any reassurance, geologists’ ideas of “a certainty” consider a geologic-scaled timeline up to thousands of years…. so life near the Sisters could well be mercifully boring during our lifetimes.

The hiking here, however, is anything but!

 

 

References:

USGS Volcanic hazards page for South Sister: https://volcanoes.usgs.gov/volcanoes/three_sisters/three_sisters_geo_hist_128.html

USGS VHP page for all Three Sisters: https://volcanoes.usgs.gov/volcanoes/three_sisters/geo_hist_south_sister.html

DOGAMI flier for Three Sisters: https://www.oregongeology.org/pubs/ll/LL-ThreeSistersRecMap.pdf

In the Playground of Giants Green Lake Field Guide http://intheplaygroundofgiants.com/field-guides-to-central-oregons-geology/field-guide-to-the-cascade-lakes-and-willamette-pass-areas/two-can-tango-recent-and-ongoing-volcanism-and-glaciation-in-the-cascade-lakes-area-field-trip-2a/optional-hiking-trails-for-field-trip-2a/

Photo Credit:

(Pika) https://www.nwf.org/Educational-Resources/Wildlife-Guide/Mammals/American-Pika

(Marmot) By Diliff – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=26414860

Many thanks to Heather van Stolk!!

 

 

 

Dome Rock and the continuing trials of Jo, the Adventure Civic

Dome Rock Hike: 10/10 would hike again, magnificent view

Drive to Dome Rock north trail head: 10/10 would NOT attempt again in a 2001 Honda Civic

I had originally planned to hike the 10-mile round trip trail from the Detroit Lake information center up the ridge to Dome Rock, but the ranger at Detroit Lake State Park was quick to discourage me. He suggested that it would be much easier to take the Forest Service road to the northern trailhead and just do the prettiest 3 mile section along the ridge top. Sure! Why not?

18% average slope on gravel roads is why. Having to stop and restart my crotchety old car multiple times on said 18% slopes to move away the fallen rocks so I could get clearance is another good reason.

Luckily the beauty of the hike brought my blood pressure back down again within a mile or so. The trail wound though firs, maples, and thimbleberries (snack time!) along the ridgetop above Tumble Lake.

Map of Dome Rock trail

Map from Willamette National Forest USFS website for trail 3381

Directions to the Tumble Creek North Trailhead can be found here on the USFS site. They aren’t kidding when they say “up steep mountain roads”.

img_20180828_115347673

At the top of Dome Rock, selfie with Tumble Lake!

img_20180828_110935026_hdr

View of Mt. Jefferson and the Three Sisters from the top of Dome Rock.

I was hiking in the Western Cascades, which form the more eroded volcanic predecessor to the striking peaks of the younger High Cascade mountains. Magma rising from the subducting Farallon plate created both zones of the Cascades, but the two stages of that subduction made them distinct. Between 35 and 8 million years ago the plate sank under North America at a slightly steeper angle, resulting in the location of the Western Cascades. Around 7 million years ago that angle became shallower, which moved the depth at which the magma rose off of the melting plate to location further east. (Devis 2013)

Inkedwestern vs high cascade Miller page 110_LI

Figure from page 110 of Marli B. Miller’s classic “Roadside Geology of Oregon” – the area of Dome Rock  is circled in yellow

change in subduction zones Miller page 113

Figure also from “Roadside Geology of Oregon”, page 113, showing how the change in subduction angle influenced the location of volcanoes further inland.

All the classic cone-shaped volcanoes of the Cascades such as Mt. Jefferson, the Three Sisters, and Mt. Hood are part of the High Cascades. In contrast, a few more million years of exposure to rivers and glaciers created the more subdued landscape of the Western Cascades. Any volcanic cones from that era have long been ground down to their roots.

img_20180828_134311232_hdr

Standing in the Western Cascades, looking at Mt. Jefferson in the High Cascade mountains. Photo taken during one of my stops to move rocks off the road…

Dome Rock itself is one of those “roots” – an isolated piece of 10 million to 17 million year old andesite where newer magma punched through a 30 million to 17 million year old area of tuff (cemented volcanic ash) and basalt. (Walker, G.W., and Duncan, R.A., 1989) It’s relative toughness meant that it withstood the 10 million years of weathering since its formation better than the surrounding formation’s softer tuff with basalt, creating the bare knob with spectacular 360 degree views.

img_20180828_122731612_hdr

Andesite near the top of Dome Rock… next time I’m hiking with my rock hammer.

Jo’s engine may have nearly overheated on the way up, but at least I didn’t have to use the engine at all for seven miles on the way down. After creeping back down the forest service road using a combination of second gear and brakes, I stopped at a peaceful little day use area along Frenchman Creek to eat my lunch. Judging by the size of the boulders in the creek bed, the stream hasn’t always been so tranquil!

img_20180828_141833842_hdr

Frenchman Creek day use area, about 1.5 miles north of the intersection with Hwy 22

Zach Urness of the Statesman wrote a helpful article on the Dome Rock/Tumble Lake hikes with more information about the lake and its campsites. I didn’t go down to the lake this time, but maybe next trip.

With all the time that skipping the extra 7 miles of the hike saved me, I stopped by Marion County’s Niagara Park on the North Santiam on the way home. My phone was dead, so no pictures this time, but if I’m by there again I’ll definitely stop to take some. The site was ambitiously called “Niagara” by hopefuls in the late 1890s aiming to build a dam where the Santiam is funneled through a 4-foot-wide crack in the underlying rocks. The dam failed repeatedly and they gave up in 1912, leaving a park with picturesque ruins. About a half-mile up the stream from the failed dam lies a  misshapen mound of rocks eroded into a perfect picnic spot and place to cool your feet off in the river.

I was sorry to have to leave the parks and head back home… and on the way back I got Jo a well-deserved car wash.

img_20180807_201542759_hdr

My sister posing with Jo the Adventure Civic on another trip that I’ll be blogging about soon!

Hiking Tumalo Creek in Bend, OR- wait, what’s that pipeline?

I could try to be coy and let you think that this snowy post happened, say, last weekend and I’m being a timely blogger who never has a backlog, but I’ll be honest. This has been kicking around since my housemate and I went adventuring over Thanksgiving break. Better late than never!

If the campground host tells you that the Tumalo Creek Campground near Bend is only going to get down to a low of 40 degrees in late November, be smarter than me and don’t believe them. On the plus-side, my friend Liz and I were so cold that we packed up camp at 7AM and were the first ones on the trail in a winter wonderland. We had the North Fork trail along Tumalo Creek all to ourselves!

trail map and bend city watershed

IMG_3218

As we hiked up to above Tumalo Falls I felt the ground crunch satisfyingly under my feet. I looked down, and saw that I was walking on these strange, fragile columns of ice! Each tuft was about 1 to 2 inches tall and supported a very thin layer of soil. I had to file it away in my head as “nature is weird”, but once I got home I found out that it’s called needle ice. This forms when the soil temperature is above freezing but the air’s is below freezing. As capillary action pulls water up through the soil it freezes in long vertical strands.

IMG_3219

Tumalo Falls! But why is it here? The sign in the parking lot has a handy explanation – this sheer cliff was created as the headwall of a glacier during the Ice Age.

24115646_10212296358136829_1546867215_o

IMG_3220

Liz was just a little happy to see the first snow on the trail as we climbed… and it got better!

IMG_3223

The trail didn’t have enough snow for snowshoes, but was precarious going in boots. We were glad for our trekking poles.

IMG_3225

After Tumalo Falls, there are several beautiful smaller waterfalls further up North Fork Trail on Tumalo Creek. This one had a prow of rock jutting out in front of it that made a perfectly scenic picnic spot.

IMG_3232

IMG_3235

We found a snowman hiding in a hollow log – a little gift from a hiker the previous day!

IMG_3238

IMG_3240

Liz contemplating another waterfall along Tumalo Creek.

That day we did the North Fork Trail as an out-and-back route, which took us from 8:30 AM to 1pm. We had hoped to make a loop with the Swampy Lakes and Bridge Creek trails, but the icy trail made for more difficult going than we had planned, and we decided to bail on the 8 mile loop in favor of a 6-mile hike. Heading back to the trailhead around 11AM we started to pass other hikers and a seemingly endless parade of their adorable dogs.

After our chilly hike, I wanted to drive down to Mt. Bachelor to see what a ski resort looked like in the winter. There might be a theme here  – being from a hometown that’s lucky to get an inch of snow, I’m fascinated by my first glimpses of snow sports! Liz kindly humored me, and we drank our pricey hot cocoa on the patio watching the snowboarders and skiers play in the disappointingly thin layer of powder. Mt. Bachelor is a ridiculously perfect dormant volcanic cone – you’ll definitely be seeing more posts about this area when I have time to read up on volcanology. Again, not a subject we have to think about much in Tennessee.

To end the day, we drove into downtown Bend to window shop in the cute town center and have dinner at Deschutes Brewery. We were just in time to watch the Oregon State University versus University of Oregon ‘Civil War’ game….ouch. The Ducks beat our Beavers 69-10. At least the delicious food and beer cushioned the blows somewhat. (The next day, I passed a church’s sign that said “Don’t worry Beavs, there’s still basketball.” Small comfort.)

I couldn’t help but notice that as we crossed the bridge to the Tumalo Creek Trailhead, a large pipe crossed the stream with us. Once in the parking lot, stern “KEEP OUT” notices shepherded us away from a gate to some new-looking buildings by the stream. To make matters more curious to this hydrologist, the trail map warned

“City of Bend Watershed:

Hiker use only (No Dogs, Stock, or Bicycles)

No Camping, No Fires”.

After some Google sleuthing, it turns out that this mysterious complex is the Heidi Lansdowne Water Intake Facility and that pipe is part of a 10-mile aqueduct that runs under Skyliner Road to the Outback Water Treatment Facility just west of Bend.

city of bend surface water system

Image showing the original 1926 Bend water systems from a 2014 presentation by Heidi Lansdowne

If we had been able to do our whole loop, we would have been hiking through the water supply area for the City of Bend! The rain that falls in this area flows down to Bridge Creek, where a portion of that water is diverted through the Intake Facility into the pipeline before the stream joins Tumalo Creek. The Heidi Lansdowne Intake Facility was built in 2016 to get the city into compliance with EPA regulations requiring filtration of surface waters.

Heidi Landsdowne Water Intake Facility

Picture of the new intake facility from Bend Water Utility

Bend has been meeting its needs with water from Bridge Creek since 1926 when it signed an agreement with the US Forest Service (USFS) allow Bend to manage the Bridge Creek Watershed. In 1926 Bend built a basic intake and filtration facility connected to a pipeline leading to town, and added an additional parallel pipeline in the 1950s. Until 2016,  Bend still relied on these two aging pipelines. In 2014 the city broke ground on the new intake facility with advanced screening to protect fish and provide a better filter to protect against elevated sediment loads caused by wildfires as well as a more modern pipeline running directly underneath Skyliner Road.

pipeline

A photo of the pipeline in progress in 2014, from the same 2014 presentation by Heidi Lansdowne

All this rambling to say that there are good reasons that this watershed is protected against:

  • Dogs – minimizing biological contamination from excrement, such as giardia
  • Stock/Cattle – minimizing fecal contamination as well, also the excess suspended sediment that they kick up in streams as they drink
  • Fires – reducing the risk that campfires will turn into wildfires that choke the streams with ash and then increase the risk of catastrophic flooding that could block the intake filters with sediment
  • Campers – because we leave embarrassing amounts of garbage behind
  • Bicycles – mountain bikes carve deeply into the trails, increasing the amount of sediment that is washed into the stream

Seeing as this is the source for much of what flows out of the taps of almost 80,000 people, it’s understandable that the public utility wants to avoid these risks.

To give you a sense of this system’s scale compared to the town, I created a map using GeoJSON.io and Mapbox.com to show Bend, the municipal watershed, the intake and treatment facilities, and the new aqueduct (the dark blue line between the facilities). GEOG 370: Cartography this term paid off!

Mapbox bend water

References:

Bend Water Utility – Bend Water Project https://www.bendoregon.gov/government/departments/utilities/stormwater/watershed

Bridge Creek Pipeline Replacement Project | City of Bend. (n.d.). Retrieved March 15, 2018, from https://www.bendoregon.gov/city-projects/city-infrastructure-projects/recently-completed-projects/bridge-creek-pipeline-replacement-project
Hammers, S. (2014, May 29). Work begins on Bend’s water treatment facility. Retrieved March 15, 2018, from http://www.bendbulletin.com/home/2114759-151/work-begins-on-bends-water-treatment-facility
No settlement on Bend water project. (n.d.). Retrieved March 15, 2018, from http://www.deschutesriver.org/media/news/no_settlement_on_bend_water_project
Park – Horse Trails Bicycle Trails.pdf. (n.d.). Retrieved from https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprd3797509.pdf
Park, S. (n.d.). Horse Trails Bicycle Trails, 1.
USFS Special Use Permit for City of Bend, October 1976, showdocument.pdf. (n.d.). Retrieved from https://www.bendoregon.gov/home/showdocument?id=33630

 

Petit Jean State Park: the outdoorsy view

To minimize my off-topic rambling, I’m covering my trip to Petit Jean State Park in two posts: this one about the hiking, and Petit Jean State Park: the nerdy perspective to cover the geology we saw along the way!

My friend Jackie and I had been trying to put together a camping getaway for a few weeks. On the recommendation of Jackie’s friends, we finally made the commitment and the three-hour drive to head west to Petit Jean SP, near Morrilton, Arkansas. It’s hard to tell from the campsite map but Jackie and I both would recommend camping in the secluded, shady Loop C and Loop D campsites over the wide open Loop A and B sites. Not that we could tell when we finally made it to the park at 11 pm.

Walking along the paths of Petit Jean State Park feels like someone took all the most gorgeous parts of four or five similarly sized parks and spliced them together into a highlights reel. Around every corner there’s a jaw-dropping view, a waterfall, a thundering 90-foot waterfall, a rock shelter, or an adorable little brook, and every patch of turtle rocks is more turtle-y than the last.  Jackie and I thought her friends were exaggerating as they described it but they sure weren’t!

You can find a full map of the trails here and of the campsites here on the park website. I went crazy in MS Paint to create the version below:

Petit Jean Annotated trail map

Petit Jean State Park has the distinction of being the first state park in Arkansas, founded in 1923 and endowed with lodges and trails by the work of the Civilian Conservation Corps during the Depression. On Saturday the two of us linked five of those trails in the park into an 8-mile loop.

IMG_2824

Jackie playing with her new camera’s settings at the overlook at the trailhead behind Mather Lodge

We started down the Cedar Falls trail early in the morning, hoping to beat the crowds. Several families were already heading downhill, and we ran into my next-door neighbors too. Small world! The trail is rocky but obviously the Civilian Conservation Corps put a lot of hard work into it – the path has dozens of rock steps. It’s beautiful too, as it follows a rocky little creek.

IMG_2828

Cedar Falls was worth every bit of the hype. Torrential rains on the Thursday and early Friday before we arrived meant that the falls were flowing at full blast! Look for the people in the photo below for scale…

IMG_2840

 

By the time we left the falls at 10:30, we felt like salmon struggling upstream as we squeezed past a solid line of families bound for the waterfall. Back at the bridge, instead of heading back up to the trail head we took the Cedar Canyon trail west. A few hundred feet past the intersection with the Cedar Falls trail we might have been in our own personal jungle – not another person in sight! This shady trail follows the creek down the valley, with some beautiful views of the flowing water, giant fallen boulders from the cliffs, and lizards hanging out on the rocks. Definitely wear long pants if you want to hike this one – the poison ivy was lush and thriving, but so were the wildflowers. We stopped at a convenient flat rock by the stream to have lunch, which we shared with a flock of very small blue butterflies.

IMG_2841

blue flowers

(Jackie’s photo)

IMG_2846

Technically, the Cedar Canyon trail dead-ends into the Boy Scout Trail at a sturdy set of stepping stones across the creek. However the massive rainstorms on Thursday and Friday which made the waterfalls so spectacular also raised the creek above the level of the stepping stones. So we got wet. The water was freezing cold and actually pretty refreshing in the noonday heat.

IMG_2849

The Boy Scout trail from the stream back up to the road is steeply uphill and an excellent leg workout. On one of our breaks to get some air back into our lungs, we met this little green tree frog taking a siesta!

treefrog

Jackie’s new camera is amazing for close-ups!!

The Seven Hollows trail is a dangerous place to go with a photographer and a rock-climbing geologist. The trail map said it was a 2 to 4 hour hike– we spent almost 6 on it. We hiked it backwards according the the trail map (counter-clockwise), which turned out to be perfect timing. Most of the families and other hikers we passed hiking to Cedar Falls did that trail as an out-and-back and then drove to the Seven Hollows trailhead to hike it clockwise after lunch. In the first mile of the trail we passed several exhausted-looking groups, and then we pretty much had our own personal trail! That first bit of our hike on that trail (Map miles 4 to 3) descended into one of the seven hollows the trail is named after – 50-foot cliffs rose on either side of the trail, full of hidden caves and swallow nests. It was so peaceful with the burbling stream at our feet and the birds singing. Not to mention, that mile is all downhill.

After “map mile” 3, the trail started to rise into the pine trees and sandstone clearings on top of the ridge. Jackie was so patient with me, because I’m the kind of person who wants to climb every boulder that I safely can, and there was no shortage of boulders.

The one downside of this trail is that it easily becomes a stream in wet weather like we had in the days before our trip, and especially from our “backwards” perspective the path that looks the nicest may actually be incorrect. Jackie and I spent an idyllic (and flat) ten minutes strolling down what turned out to be a trail to private property before noticing the absence of blue blazes. We retraced our steps to discover we should have taken the left-hand fork: the nearly vertical, soaking wet, bare rock face that was actually the trail. Oops.

That slippery slope is totally worth it, though because it leads to the highlight of this section of the trail: The Grotto. You reach it via a narrow, rocky spur off of the main trail that opens up into a rock shelter and cascade that look like a scene straight out of The Land Before Time.

IMG_2861

I took a side trail up above the falls, and found a whole herd of turtle rocks!

IMG_2865

After the Grotto, the trail turns back uphill has we climbed up the last ridge that the trail crosses before heading north to the trailhead. The peak of this part of the trail has more sandstone clearings and beautiful views to the southeast.

Jackie and I were in a hurry, though, to reach the last big landmark of the hike – a natural bridge. It lived up to the expectations! We hung out there for a while, refueling with trail mix and exploring all the nearby rock formations. For more on how arches like this are formed, you can check out my Red River Gorge post here. Same process, different sandstone!

IMG_2869

can i climb it full view

Contemplating whether I was feeling rash enough to free-solo my way up to the top of the cliff by the arch. I decided I wasn’t. It was SO tempting though.

There aren’t any more landmarks noted on the park map after the natural bridge, but if you keep your eye out there are two caves in the sandstone cliff on between the bridge and the trail head. After the two caves, at about “map mile” 0.5, there’s a well-beaten path that appears to dead-end in a cliff wall. If you take a sharp left at the “dead-end” and are comfortable scaling a short 5.4 climb, there are some spectacular turtle rocks up top and you can see for miles. The golden late-afternoon light and our haze of exhaustion made it really seem magical. Jackie and  obviously need to hike more often so 7 miles doesn’t turn our legs to jelly.

IMG_2873

IMG_2874

The only downside of the Seven Hollows trail is that it ends in a long uphill climb whichever direction you do it in.  Another mile up the trail we basked for a while in the evening sun, like two very tired lizards, on top of the rock formations at Bear Cave before making the last 1/2 mile push to the end.

IMG_2881IMG_2883

^ The view from the top of the Bear Cave area, and Jackie climbing down

We celebrated with soda and junk food at Mather Lodge around 7pm and then drove back to Bear Cave for a great tour of the area with interpreter BT Jones and 53 other visitors. It was definitely worth it to hear the stories of the pioneer days of the area and to make a giant echo off of the walls of Cedar Creek Canyon.

We slept very well that night, and threw out the pipe dream of waking up to see the sunrise. We got up just early enough to pack up camp and start the Cedar Creek loop trail bright and early at 8 AM, when we had it all to ourselves! This trail is has a brochure that indicates that it’s a self guided tour (you can find it here), but Jackie and I couldn’t find stops 3, 4, or 5. The entire trail look like Middle Earth in the early morning light, it was really magical.

IMG_2891

Jackie at a beautiful place for a snack break

IMG_2893

The leaning rock along the Cedar Creek trail

IMG_2901

Textbook-perfect ripple marks in the sandstone on the southern leg of the trail

After lingering on this loop for an hour and a half, we piled back into the car for a driving tour around the overlooks in the park.

IMG_2907

Jackie at the Cedar Falls Overlook. Not only is it beautiful but it’s handicap accessible too.

IMG_2913

At the M.A. Richter Memorial Overlook you can see all the way to Mount Magazine, the highest point in Arkansas, 50 miles away!

IMG_2924

Jackie enjoying the view at the CCC Overlook

IMG_2925

The CCC shelter at the CCC Overlook – there’s a lawn to the right of it that would make an absolutely perfect picnic spot.

We had one last hiking stop – the trail down to the Rock Cave archaeological site. It winds through a phenomenal field of turtle rocks…

IMG_2928

There must have been dozens of them!

exploring the rock house

You could easily fit a football field inside this rock shelter, no joke. (Jackie’s photo)

IMG_2931

One of the several Native American paintings in the shelter, drawn with red iron oxide paint over 500 years ago.

Jackie and I had one last stop as we headed out of the park: Stout’s Point and Petit Jean’s gravesite.

The name of Petit Jean Mountain and its park have a sweet and possibly even true backstory. The area was first explored by French traders, and the story goes that one of these traders had a particularly devoted sweetheart. Unbeknownst to him, who would have forbidden her to come if he knew, she sneaked onto his ship in the guise of the cabin boy “Petit Jean”. Her disguise held up and she was able to at least be close to him until the story took a tragic turn as they headed up the Arkansas river. She came down with a sudden illness, and only as she was dying did those caring for her discover her secret. Her last wish was to be buried on top of the magnificent lookout she saw from the river, and her grieving trader carried it out.

That lookout is now called Stout’s Point, after the Episcopal minister who led the effort to settle the mountain with white pioneers.

view from stout's point

The view of the Arkansas River from Stout’s Point

IMG_2938.JPG

Jackie and I didn’t want to leave the park – we agreed that we needed a break in the space-time continuum to add another day to the weekend. Unfortunately we had to face reality and head back east, but now Petit Jean State Park has two more passionate promoters!

CCC overlook both of us

All of Jackie’s photos are cc Jacqueline Arevalo

A Tale of Two Sandstones: Giant City State Park

Earlier this month I found myself driving though the hills of southern Illinois, and decided to take an extra time to spend some quality time with the topographic relief and exposed rock that us residents of western Tennessee don’t see very often.  I spent the morning rambling though Giant City State Park south of Carbondale, and didn’t want to leave! I wandered around the Giant City Nature Trail, which is only officially 1.5 miles but probably more like 3 if you take all the side-trails. After that I stopped by the short Devil’s Standtable trail on a whim, and I’m glad I did! It follows the base of a gorgeous cliff line, and has ample opportunities for scrambling and climbing.

IMG_2791

This strategically place trail sign with geologic information might dissuade you from exploring further, but take the well-traveled unofficial trail past it to get to a waterfall!

Southern Illinois is a island of rugged terrain in a state where the elevation rarely exceeds “rolling hills”. It barely managed to escape the Wisconsonian glaciation which bulldozed Illinois north of Highway 13, creating prime cornfield habitat north of the highway and a maze of deep valleys, tall sandstone cliffs, and forested ridges south of Carbondale and Harrisburg. All in all, this section feels more like a misplaced chunk of the Ozarks.

It occurred to me, while eating my lunch on top of a stray sandstone boulder, that the landscape look like a miniature version of the Cumberland Plateau 300 miles to the east. (You can see where those rocks come from in my Red River Gorge Post) These sandstone outcrops had the same iron bands, fragmented blocky weathering structure, and selection of trees clinging tightly to their cliffs. This made me wonder – are these rocks part of the same depositional unit as the ones on the Cumberland Plateau, or do they have a different source but just happen to look similar?

IMG_2781

A particularly enterprising tree along the Giant City Nature Trail

Callan Bentley did a great breakdown of the geologic features of the sandstone of the park over at the AGU blog. It turns out that the lacy weathering structure that I had been calling “honeycomb” has the snazzy official name of “tafoni”! I don’t think I can beat Callan’s beautiful photographs and blow-by-blow of depositional features, but I couldn’t find a source for my origins question and set out to research it.

It turns out that the rocks I was admiring, clambering on, and using as a picnic bench were part of the Chesterian formation of sedimentary rocks laid down during the second half of the Mississippian period roughly 359 to 323 million years ago. Therefore, they’re roughly the same age as the rocks on the Cumberland Plateau which were laid down during the Carboniferous era (which is divided the Mississippian period followed by the Pennsylvanian Period).

The rocks in Giant City State Park are on the western edge of what’s called the Illinois Basin, a regional depression in the crust exacerbated by large amounts of sediment deposited when the region was covered by a shallow sea until the Late Pennsylvanian period ~300 million years ago. This same sea also covered the area now occupied by the Cumberland Plateau, and its waves crashed against the shores of the vast deltas carrying sediment down from the rising Acadian orogen of the current Appalachian mountains. The rocks in the Red River Gorge of eastern Kentucky aren’t in the same “family” as the rocks in Giant City State Park, in the sense that they don’t share a sediment source, but instead are classmates from different origins maturing together through geologic time.

There was a bit of a speed bump that separated the Illinois Basin from the Appalachian Basin – the Cincinnati Arch. Now, as we get acquainted with this speed bump, there’s something to keep in mind. Although the older Ordovician rocks at its core might indicate that it’s an anticline (a convex fold in sedimentary layers), this cross section has a trick up its sleeve.

cinArch

This diagram shows a vertically exaggerated cross-section of the types of bedrock in Kentucky, show that the rocks of the Appalachian Basin (Cumberland Plateau) are separated from the rocks of similar age in western KY/Southern IL by the Cincinnati Arch.

The Cincinnati Arch isn’t a fold structure, but a strip of crust that maintained its original elevation  while the regions to the east and west sagged under the weight of sediment that was piling onto them. I couldn’t find primary resources resource to mention why exactly the Cincinnati arch was able to avoid being down-warped by sediments as its eastern and western neighbors were, unfortunately. (If you know more about that, please contact me!)

That cross-section sparked my interest, so I set out to find a paleogeographic map of North America during the Mississippian period when the Illinois Basin and Cumberland Plateau sandstones were being dumped into place. This map shows a reconstruction of the Early Mississippian, so sea levels would have been a bit lower in the mid- to late- Mississippian period when the Chesterian rocks were laid down.  About 1/3 to 1/2 of northern Illinois would have been above the waves.  I fancied it up in CorelDraw to show the arch, basins, and approximate directions of sediment transport into the basins…

Annotated Mississippian Map 4

Looking at the map, you notice that the arrows pointed to the Appalachian basin come from a mountainous region, and the ones pointing towards Illinois come from part of the land surface that’s relatively flat. This is reflected in the depth of sediment with each basin – the sandstone layers in Illinois are thinner than those in eastern Kentucky. Conversely, because the Illinois basin contained a slightly deeper sea with less sediment input it has thicker layers of limestone in the Carboniferous deposits than the Appalachian basin.

The limestone of the Illinois basin is a major economic resource in the area. Driving down Highway 51 leaving the park (sigh…) I passed the Anna Quarry Company, which has been profiting from that ancient Carboniferous sea since 1865. Their 200-acre, 450-foot deep original mining pit was abandoned when it became economically unfeasable (let’s just say, it now has 350 feet of water in it) but they continue to mine new pits on the property to provide raw materials for aggregate, asphalt, concrete, and agricultural lime.

IMG_2800

I got some really funny looks as I parked along the highway to take photos…

Anna Quarry

An aerial view of the Anna Quarry in Anna, Illinois

It was a beautiful sunny drive back to Memphis, but I need to drag some friends back to Jackson Falls in this same area to climb soon!

Sources:

Giant City State Park website: https://www.dnr.illinois.gov/Parks/Pages/GiantCity.aspx

breakdown of geological formations: http://blogs.agu.org/mountainbeltway/2011/09/20/giant-city/

Chesterian sandstone, which includes the rock at the park: http://isgs.illinois.edu/ilstrat/index.php/Chesterian_Series

A retro but generally accurate backstory of the geology of southern Illinois: https://www.ideals.illinois.edu/handle/2142/42765

A more approachable take on the ancient landscapes of Illinonis: https://www.isgs.illinois.edu/outreach/geology-resources/build-illinois-last-500-million-years

Source of KY cross section: https://www.uky.edu/KGS/geoky/beneath.htm

Source of paleogeographic Mississippian map: http://deeptimemaps.com/wp-content/uploads/2016/05/NAM_key-345Ma_EMiss.png

Source for information on Cincinnati Arch: http://ncad.net/Gp/Erla/ErlaGeol.htm

Blog post about Cincinnati Arch: http://historyoftheearthcalendar.blogspot.com/2014/03/march-10-cincinnati-arch.html

Bedrock Geology of Illinois Map: http://isgs.illinois.edu/sites/isgs/files/maps/statewide/imap14-front.pdf

Bedrock Geology of Illinois Strategraphic Sequence: http://isgs.illinois.edu/sites/isgs/files/maps/statewide/imap14-back.pdf

http://www.resolveexploration.com/Geo_History.htm

https://www.isgs.illinois.edu/outreach/geology-resources/building-bedrock