Geology of Devils Tower National Monument Wyoming _By_ CHARLES S. ROBINSON A CONTRIBUTION TO GENERAL GEOLOGY [Illustration: DEPARTMENT OF THE INTERIOR · March 3, 1949] The National Park Service and the Devils Tower Natural History Association wishes to thank the United States Geological Survey for their kind permission to have this Bulletin reprinted with minor changes. CONTENTS Page Abstract 1 Introduction 1 Geology 3 Devils Tower 3 Sedimentary rocks 6 Spearfish formation 6 Gypsum Spring formation 7 Sundance formation 7 Stockade Beaver shale member 8 Hulett sandstone member 8 Lak member 9 Redwater shale member 9 Stream terrace deposits and alluvium 10 Talus and landslide material 10 Structure 11 Geologic history 11 Origin of Devils Tower 12 Selected bibliography 13 ILLUSTRATIONS FIGURE Page 52.—Index map showing location of Devils Tower National Monument 2 53.A.—Northwest side of Devils Tower showing how the columns taper or converge and in places unite near the top and are cut by numerous cross-fractures 4 B.—Southwest corner of Devils Tower showing the columns flaring out and merging to form the massive base 4 54.—Generalized section of the sedimentary rocks of the Devils Tower National Monument 6 A CONTRIBUTION TO GENERAL GEOLOGY GEOLOGY OF DEVILS TOWER NATIONAL MONUMENT, WYOMING By Charles S. Robinson ABSTRACT