The Chinle Dormitory is named after the Chinle Formation. The Chinle Formation formed about 215 million years ago during the late Triassic Period and is 350-640 feet thick. A period of increased moisture caused streams, lakes, marshes and floodplains to leave behind deposits of silt, mud, and fine sands. This formation is easily identified by the gray and purple coloration along its slopes. It is well known for containing petrified wood as well as uranium deposits.