Skip to Main Content
Book Chapter

5: Overview of the Eocene Castle Rock Conglomerate, east-central Colorado: Remapping the fluvial system, and implications for the history of the Colorado Piedmont and Front Range

By
Stephen M. Keller
Stephen M. Keller
Colorado Geological Survey, Colorado School of Mines, 1801 19th Street, Golden, Colorado 80401, USA
Search for other works by this author on:
Matthew L. Morgan
Matthew L. Morgan
Colorado Geological Survey, Colorado School of Mines, 1801 19th Street, Golden, Colorado 80401, USA
Search for other works by this author on:
Published:
January 01, 2016

Abstract

The Castle Rock Conglomerate is a late Eocene fluvial deposit flanking the east side of the Colorado Front Range and lying within the Colorado Piedmont. It occurs as a northwest-southeast–trending swath ~63 km in length and between 3 and 10 km in width, and is ~70 m in thickness. The conglomerate consists of a matrix of arkosic coarse sand and granules along with pebble- to boulder-sized clasts that vary in abundance. Locally, the upper portion of the conglomerate is well exposed in cliffs and ledges and also in flat outcrops along drainages. Large to very large-scale cross- bedding, of both the planar and trough types, is characteristic of the unit. Clasts are dominantly Front Range granitic rocks and Wall Mountain Tuff, and boulders of the latter can exceed 0.5 m in diameter. Minor quantities of quartzite and vein quartz, and rare sedimentary clasts, also are present. The large sizes of the bedforms and clasts indicate deep water and high velocity during deposition. A recent, extensive paleocurrent study of the upper part of the conglomerate has produced a new map of the fluvial system, indicating a main, southeast-trending paleochannel with two major northeast-trending tributaries. This field trip will present an overview of the Castle Rock Conglomerate lithology, bedforms, and associated geologic units; ideas about its deposition; and its bearing on uplift along the Front Range and in the southwest Denver Basin. Planned stops will be in Douglas and Elbert Counties, south of Denver, and include Castlewood Canyon State Park, Prairie Canyon Ranch open space, private farm and ranch properties, and an inactive quarry. Several of the stops provide excellent vistas of the Front Range, majestic Pikes Peak, and also of the Colorado Piedmont.

You do not currently have access to this article.

Figures & Tables

Contents

GSA Field Guide

Unfolding the Geology of the West

Stephen M. Keller
Stephen M. Keller
Colorado Geological Survey Colorado School of Mines 1801 19th Street Golden, Colorado 80401, USA
Search for other works by this author on:
Matthew L. Morgan
Matthew L. Morgan
Colorado Geological Survey Colorado School of Mines 1801 19th Street Golden, Colorado 80401, USA
Search for other works by this author on:
Geological Society of America
Volume
44
ISBN print:
9780813756448
Publication date:
January 01, 2016

GeoRef

References

Related

Citing Books via

Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal