About 500 million years ago, Wyoming, including this area, lay beneath seas in a warmer world where no animal life lived on land. Around 75 million years ago, grinding in the earth’s crust caused the land to buckle and heave, forming the Big Horn Mountains. The long, sharp red ridges here are called hogbacks, and the surrounding geology also includes steep escarpments along the fault on this side of the Big Horn Mountains, synclines that create valleys, and cuestas, long gentle upslopes of alternating hard and soft rocks.