The Geological History of Fossil Butte National Monument and Fossil Basin

As the Nation’s principal conservation agency, the Department of the Interior has basic responsibilities for water, fish, wildlife, mineral, land, park, and recreational resources. Indian and Territorial affairs are other major concerns of America’s “Department of Natural Resources.” The Department works to assure the wisest choice in managing all our resources so each will make its full contribution to a better United States—now and in the future.
This publication is one in a series of research studies devoted to special topics which have been explored in connection with the various areas in the National Park System. It is printed at the Government Printing Office and may be purchased from the Superintendent of Documents, Government Printing Office, Washington, D.C. 20402.
Library of Congress Cataloging in Publication Data
McGrew, Paul Orman, 1909- The geological history of Fossil Butte National Monument and Fossil Basin. (National Park Service occasional paper; no. 3) Bibliography: p. Includes index. 1. Geology—Wyoming—Fossil Butte National Monument. 2. Geology, Stratigraphic—Eocene. 3. Paleontology—Eocene. 4. Fossil Butte National Monument, Wyo. I. Casilliano, Michael, joint author. II. Title. III. Series: United States. National Park Service. National Park Service occasional paper; no. 3. QE182.F67M3 557.87'82 75-17511
Paul O. McGrew Michael Casilliano Department of Geology, University of Wyoming
NATIONAL PARK SERVICE OCCASIONAL PAPER NUMBER THREE
Fifty million years ago the southwestern corner of what is now Wyoming was part of a system of three freshwater lakes that covered that area plus adjacent parts of Colorado and Utah.
The shores surrounding the lakes were blanketed by a lush, green canopy of palm, cinnamon, maple, oak, and other familiar trees. Hazel and lilac covered the forest floor. Rushes and other aquatic plants lined the lake shore.
The air was humid and warm. Streams flowing down from the hills and mountains built up flood plains and fed sediment into the lake, where it was deposited in shallow water near the shore. Deposits formed by chemical processes settled to the bottom further from shore in deep, quiet water. From these processes were formed the rocks from which the past history of Green River Lake System is read.