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Open-File Report 2011-1111

Preliminary Geologic Map of the Bowen Mountain Quadrangle, Grand and Jackson Counties, Colorado

By James C. Cole, William A. Braddock, and Theodore R. Brandt

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Abstract

The map shows the geology of an alpine region in the southern Never Summer Mountains, including parts of the Never Summer Wilderness Area, the Bowen Gulch Protection Area, and the Arapaho National Forest. The area includes Proterozoic crystalline rocks in fault contact with folded and overturned Paleozoic and Mesozoic sedimentary rocks and Upper Cretaceous(?) and Paleocene Middle Park Formation. The folding and faulting appears to reflect a singular contractional deformation (post-Middle Park, so probably younger than early Eocene) that produced en echelon structural uplift of the Proterozoic basement of the Front Range. The geologic map indicates there is no through-going "Never Summer thrust" fault in this area. The middle Tertiary structural complex was intruded in late Oligocene time by basalt, quartz latite, and rhyolite porphyry plugs that also produced minor volcanic deposits; these igneous rocks are collectively referred to informally as the Braddock Peak intrusive-volcanic complex whose type area is located in the Mount Richthofen quadrangle immediately north (Cole and others, 2008; Cole and Braddock, 2009). Miocene boulder gravel deposits are preserved along high-altitude ridges that probably represent former gravel channels that developed during uplift and erosion in middle Tertiary time.

First posted June 28, 2011

For additional information contact:

USGS Geology and Environmental Change Science Center
Box 25046, Mail Stop 980
Denver, CO 80225

http://esp.cr.usgs.gov/

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Suggested citation:

Cole, J.C., Braddock, W.A., and Brandt, T.R., 2011, Preliminary geologic map of the Bowen Mountain quadrangle, Grand and Jackson Counties, Colorado: U.S. Geological Survey Open-File Report 2011–1111, 15 p., scale 1:24,000.



Contents

Abstract

Geologic Mapping

Stratigraphic Notes

Structure

Oil Exploration

Acknowledgments

References Cited

Description of Map Units

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