Ancient quarries


  • Elaine Friebele


Using a unique set of remote sensing techniques, a team of University of Colorado researchers has detected mining pits dug by Montana Indians 10,000 years ago. The team used satellite images, aerial photographs, and ground tests to locate quarries where ancient North Americans obtained chert for making tools.

Anthropology doctoral student Thomas Carr, Mort Turner, of the University of Colorado's Institute of Arctic and Alpine Research, and four undergraduate and graduate students developed 12 “spectral classes” characterizing distinct geologic and vegetation types found in the Horse Prairie Valley study area in southwest Montana. Their data included electromagnetic measurements of soil conductivity from a known Indian quarry in the area, where the altered bedrock contains veins of chert, and an adjacent area of disturbed soil. Using special computer software, the team compared characteristics of nearly one million 30-m2 pixels from a 1985 regional Landsat satellite image to those of the 12 spectral classes. Twelve possible ancient mining sites in the 800-square-mile research area were identified. During a later ground survey using GPS satellite receivers, eight of these were confirmed to be ancient Indian quarries.