Stone tool fragments discovered in 1965 and 1972 on the shores of Lake Theo led to archeological testing in 1974 that revealed a campsite and a bison butchering and processing area dating to the age of Folsom man, between 10,000 and 12,000 years ago. Projectile points and scraping tools were found at a depth of four feet along with over 500 bones from an extinct type of bison. Ponds in Holmes Canyon, now covered by Lake Theo, probably attracted prehistoric men to this area.