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Unusual Geology
Walking on quartzite stones sounds different. The shifting rock feels - somehow unique. When you walk on the loose scree (accumulation of rock debris at the base of a slope) around Devil’s Lake, your footfall scrunches with an almost musical clink and scrape of broken stoneware pottery. Underfoot, it doesn’t sound like a crushed limestone gravel driveway. The rock is older than you. It’s tougher than you. It’s shifting, but not yielding, not giving up even a single chip of its structural integrity.
You will pass, but the rocks will remain long after you are gone
Devil’s Lake quartzite is some of the hardest rock on earth. The quartzite rock began long ago as draining rivers brought quartz sand into shallow seas in this region. Over vast lengths of time, water circulating with silica, carbonate and iron oxide bonded the sand particles together into sedimentary sandstone. Then trillions of tons of pressure compressed the
sandstone into a metamorphic (changed) rock called quartzite. The seas left the area, and an uplift slowly formed what we call the Baraboo Hills into a canoe-shaped ellipse about 25 miles long and 5 miles wide. The middle of the “canoe” filled with softer sedimentary rock composed of sand and lime. Water draining from this oval plateau unhurriedly cut through the upturned edges of the Baraboo hills, forming what we now call the Devil’s Lake gorge and the lower narrows of the Baraboo River. Eventually, most of the softer sandstone and limestone eroded away, leaving a long oval depression surrounded by the Baraboo Hills. You may have driven through Lower Narrows State Natural Area coming into Baraboo on Highway 33 from the 90/94 Interstate.
Glaciers did NOT carve the valley
Wisconsin’s renowned glaciers wielded their influence on the Devil’s Lake story about 15,000 years ago. Walls of ice hundreds of feet thick bulldozed their way from a frozen northland, flattening and smoothing entire landforms along the way. The inexorable sculpting snout of two glacier lobes ground to a halt at either end of the Devil’s Lake valley, leaving dam-like piles of
earth, gravel, and rock called terminal moraines. (Visit the Nature Center, which sits atop one terminal moraine. Then go to Roznos Meadows on Highway 113 and look west to see the textbook view of the other terminal moraine, stretching across the valley in the distance). Finally the stage was set for the small footprint of a lake to be framed between the rugged quartzite bluffs. Devil’s Lake is an endorheic lake, having no natural drainage outlet. Its 360 acres are supplied solely by local drainage and springs. The maximum lake depth is usually 45 – 48 feet.
500’ to the bluff tops
Five hundred feet make a difference. In early and late winter snowfalls, with the air temperature near freezing, it’s not unusual for any snow accumulation at lake level to be exceeded by 20% to 50% on the bluff tops. The slanting fields of boulders (talus slopes) along the lake shores were formed by freezing and thawing tirelessly loosening rocks until they shattered and tumbled. The signature formations of Balanced Rock and Devil’s Doorway were formed by this slow process. In the summer, on the Grottoes Trail visitors have long appreciated the cooled air sinking through the talus boulders, flowing out as natural air conditioning at the
bottom of the boulder field.
Geology may be old and dusty but it’s not dull!
Here are a few tidbits to whet
your geological appetite for the area. The highest point in the park is neither on the East Bluff nor on the West Bluff, and few people ever stand there. It’s five miles east of the lake near the radio towers above the Sauk Point Trail. Take a walk in Parfrey’s Glen State Natural Area to find strange “pudding stone” – chunks of metamorphic rock embedded within sedimentary sandstone rock. In Steinke Basin find the reddish rhyolite boulder (north of the old windmill frame) an oddity brought all the way from Canada by the Wisconsin glacier. Or stand in an acre-sized deep kettle left by a collapsing glacial ice block. Outside the park, drive a few miles to Ableman’s Gorge State Natural Area near Rock Springs and see the world renowned Van Hise Rock, which made apparent one of the defining ideas of historical geology. Take a side trip to the Natural Bridge State Park and see the natural arch rock-shelter used by prehistoric peoples 12,000 years ago. Find Pewit’s Nest State Natural Area and imagine the one-of-a-kind house that was once built above the stream between the narrow rock walls of a ravine. Check these out!
Photo By: D. Thomas from 2011 Photo Contest
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