.TOURING
COLORADO GEOLOGY
Pre-Cambrian
/ Fountain Roadcut|
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.TOURING COLORADO GEOLOGY |
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Pre-Cambrian
/ Fountain Roadcut |
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Along Highway 285, just south of the Morrison exit, the Fountain Formation (Carboniferous) lies unconformably on the Pre-Cambrian Idaho Springs Formation. A hiatus of approximately 300 million years exists here (1.1 billion years to 350 million years). Although there is very large expanse of time missing, the contact is not readily apparent. This is due in part to the fact that the lowermost Fountain is composed of the eroded Pre-Cambrian Idaho Springs Formation.
| An overview of the roadcut to the right. Not extremely impressive as roadcuts go. It is also not a particularly safe stop. You can pull off ok just west of the contact, but it is on a curve and by the time you walk back to the contact, you are forced almost out to the edge of the road with traffic speeding by very close. The contact is somewhere between the truck and the right edge of the picture. |
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To the left are Pre-Cambrian rocks - to the right are sedimentary rocks of the Fountain. They don't look all that different, do they? Veins in the rocks on the left are a give-away for Pre-Cambrian. |
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In the picture to the right,
you can see the work of some geologist who has drilled a number of holes
in the granite for analysis. This granite is quite
interesting. Note the large biotite grains in the granite. |
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