In the end of September I took a trip to Devils Lake State Park located in the Baraboo Hills, Wisconsin. For the twenty years before that trip I went for weekend camping trips; My time was spent hiking, canoing, rappelling and spending time with family and friends.
This time I visited to study the geology. I am surprised how different the world looks when I open my eyes as a geologist.
I walked on the trails and stepped on the rocks countless times, but it is all different to me now.
Now Devils Lake is more than my favorite state park...it is a geologic goldmine.
For Part I of my Devils Lake series I will talk about the formation of the Baraboo Hills and the Devils Lake gorge.
The Precambrian Baraboo Quartzite is about 1.7 billion years old. The approximately 4,000 foot layer is formed from metamorphosed quartz sandstone that was deposited by braided rivers and shallow seas. It is very homogeneous and contains iron oxides that give the rock it's red coloring.
The theory is that around 1,650 million years ago a continental collision deformed the rocks into a series of folds. During this folding the sandstones were metamorphosed into quartzite, as well as the other layers were metemorphosed into their proper metamorphic form. The North Range and South Range are exposed portions of the folded quartzite, with a downfold between them that cradles 1,500 feet of Precambrian Strata including slate, dolomite and banded iron formation. Although, none of these strata are exposed in this area.
Sometime during the late Precambrian a river cut through the south range of the Baraboo Hills carving out an 800 foot deep valley. This valley is now home to Devils Lake.
Don't get too excited yet, before we can even think about the actual lake and the present day landscape we must talk about the Potholes, Cambrian oceans and the Quaternary Ice Age!
Next time I will have pictures and I will be discussing the Potholes as well as the Cambrian time period when the tops of the Baraboo Hills were all islands and powerful tropical storms battered the sea cliffs of red quartzite (as well as how the oceans deposited sedimentary strata that buried the Baraboo Hills almost entirely about 440 million years ago). |
