Preliminary geologic map of the Pumpkin Buttes area, Campbell and Johnson Counties, Wyoming, showing location of uranium occurrences

The Pumpkin Buttes area comprises about 450 square miles in Campbell and Johnson Counties that includes several prominent buttes known as Pumpkin Buttes.  The area is near the center of the Powder River Basin, a large physiographic unit of prairie and sculptured terrain that occupies approximately 12, 000 square miles of northeastern Wyoming.  The basin is bounded on the east by the Black hills, on the south by the Laramie Mountains, and on the west by the Big Horn Mountains.  The northern end is more or less open into Montana.  Much of the basin ranges in altitude from 4,000 to 5,000 feet above sea level; but in the central part, about 40 miles southwest of Gillette, the Pumpkin Buttes rise abruptly to an altitude of 6,000 feet.

Secondary uranium minerals were discovered in the vicinity of Pumpkin Buttes in October 1951 (Love, 1952).  The following spring, a study of the area and the uranium occurrences was begun by the Geological Survey on behalf of the Division of Raw Materials of the U. S. Atomic Energy Commission.  The accompanying map, which shows distinguishable lithologic units and occurrences of uranium in outcrop, is a result of the continuation of this study.