During portions of the summers of 1905 to 1907 I made a reconnaissance of the geology of parts of central Wyoming, extending from the Colorado state line southwest of Laramie to the Wind River mountains northwest of Lander. Detailed geologic maps were made of much of the region lying east of longitude 107° and south of latitude 43°, and the Laramie and Sherman quadrangles of the U. S. Geological Survey were prepared for folio publication. In the western portion of the area I was assisted by Mr E. G. Woodruff, and most of the data in the region southwest of Laramie and Cheyenne were obtained for me by Mr C. E. Siebenthal. The work was a continuation southward of my explorations in the Bighorn and Owl Creek uplifts, which have been published by the government. 23
It is the purpose of this memoir to present an outline of . . .