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Scientific Investigations Map 3267

Geologic Map of the Harvard Lakes 7.5’ Quadrangle, Park and Chaffee Counties, Colorado

By Karl S. Kellogg, Keenan Lee, Wayne R. Premo, and Michael A. Cosca

Thumbnail of and link to report PDF (26.9 MB)Abstract

The Harvard Lakes 1:24,000-scale quadrangle spans the Arkansas River Valley in central Colorado, and includes the foothills of the Sawatch Range on the west and Mosquito Range on the east. The Arkansas River valley lies in the northern end of the Rio Grande rift and is structurally controlled by Oligocene and younger normal faults mostly along the west side of the valley. Five separate pediment surfaces were mapped, and distinctions were made between terraces formed by the Arkansas River and surfaces that formed from erosion and alluviation that emanated from the Sawatch Range. Three flood deposits containing boulders as long as 15 m were deposited from glacial breakouts just north of the quadrangle. Miocene and Pliocene basin-fill deposits of the Dry Union Formation are exposed beneath terrace or pediment deposits in several places. The southwestern part of the late Eocene Buffalo Peaks volcanic center, mostly andesitic breccias and flows and ash-flow tuffs, occupy the northeastern corner of the map. Dated Tertiary intrusive rocks include Late Cretaceous or early Paleocene hornblende gabbro and hornblende monzonite. Numerous rhyolite and dacite dikes of inferred early Tertiary or Late Cretaceous age also intrude the basement rocks. Basement rocks are predominantly Mesoproterozoic granites, and subordinately Paleoproterozoic biotite gneiss and granitic gneiss.

First posted December 31, 2013

For additional information, contact:
Director, Geosciences and Environmental Change Science Center
U.S. Geological Survey
Box 25046, Mail Stop 980
Denver, CO 80225
http://gec.cr.usgs.gov/

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Suggested citation:

Kellogg, K.S., Lee, Keenan, Premo, W.R., and Cosca, M.A., 2013, Geologic map of the Harvard Lakes 7.5' quadrangle, Park and Chaffee Counties, Colorado: U.S. Geological Survey Scientific Investigations Map 3267, 22 p., scale 1;24,000, http://dx.doi.org/10.3133/sim3267.

ISSN 2329-132X (online)



Contents

Abstract

Geologic History

Description of Map Units

Acknowledgments

References Cited


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