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Scientific Investigations Map 3156

Geologic Map of the Bailey 30’ × 60’ Quadrangle, North-Central Colorado

By Chester A. Ruleman, Robert G. Bohannon, Bruce Bryant, Ralph R. Shroba, and Wayne R. Premo

Thumbnail of SIM 3156 Pamphlet to Accompany MapAbstract

The Bailey, Colo. 1:100,000-scale quadrangle lies within two physiographic and geologic provinces in central Colorado: 1) the Front Range and 2) South Park. Most of the Front Range is composed of Proterozoic rocks ranging in age from 1,790 Ma to 1,074 Ma. Along the eastern flanks and within the Denver Basin, sedimentary rocks ranging from Pennsylvanian to Cretaceous are deformed and steeply tilted to the east. Upper Cretaceous through Paleocene rocks were deposited in the foreland (that is, the Front Range eastern flank) and hinterland (that is, South Park) of this thrust and reverse fault system developed during the Late Cretaceous to Paleocene Laramide orogeny. Within South Park, rocks range in age from Pennsylvanian to Miocene with Quaternary deposits indicating tectonic subsidence of the basin. These rocks record five major geologic episodes: 1) the Paleozoic Anasazi uplift that formed the Ancestral Rockies, 2) the Late Cretaceous to Paleocene Laramide orogeny, 3) widespread Eocene to Oligocene volcanism, 4) Oligocene–Quaternary tectonics, and 5) Quaternary glacial episodes.

First posted November 21, 2011

For additional information contact:

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

Part of this report is presented in Portable Document Format (PDF); the latest version of Adobe Reader or similar software is required to view it. Download the latest version of Adobe Reader, free of charge.

Suggested citation:

Ruleman, C.A., Bohannon, R.G., Bryant, Bruce, Shroba, R.R., and Premo, W.R., 2011, Geologic map of the Bailey 30’ x 60’ quadrangle, North-Central Colorado: U.S. Geological Survey Scientific Investigations Map 3156, scale 1:100,000, pamphlet, 38 p.

Pamphlet Contents

Description of Map Units

Geologic History of the Bailey Quadrangle


References Cited

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