STS068-249-039 Bighorn Mountains, Wyoming, U.S.A. October 1994 Formed 55 to 60 million years ago, the Bighorn Mountains shown in this southwest-looking, low-oblique photograph consist mostly of basement rocks more than 1 billion years old. The fault-thrust, glacier-carved range extends approximately 120 miles (195 kilometers) from the Pryor Mountains of south-central Montana (not visible) southeastward to the Bridger Mountains of central Wyoming (not visible). Snow covers the higher peaks of the Bighorn Mountains throughout the year; forests cover the lower slopes; and wildlife is abundant throughout the mountains. To the west are the Bighorn Basin and the Bighorn River with irrigated agricultural areas in its valley. Visible east of the Bighorn Mountains are the western portion of the Powder River Basin; long, narrow Lake De Smet; and Sheridan (barely discernible) on Goose Creek. To the north are the Wolf Mountains of south-central Montana (bottom right).