Bison Rockshelter is one of the two most significant archaeology sites found within the Birch Creek area, the other being Veratic Rockshelter (10CL3) which lies just to the North. These shelters were discovered during the Birch Creek Archaeology Project which revealed 136 archaeology sites, including 54 open camp sites, 77 rockshelters, 1 "tipi ring," and 4 circular rock structures (Swanson 1964). The geological formation of the two previously mentioned rockshelters was begun by the erosive action of Birch Creek as it flowed against the rock face during the late Pleistocene. The shelters were enlarged to their present size by the process of insolation, frost, weathering, and structural failure. They were eventually partially filled by alluvial fan deposits (Swanson 1972). The Birch Creek Project was conceived by Earl H. Swanson Jr. to test his theories regarding the prehistory of the Shoshonean speaking peoples of the Northern Rocky Mountains. Swanson believed that the spread of Shoshonean dialects could be explained as traveling South and Westward out of the Rocky Mountains as well as diverging from the dialects spreading in a North and Eastward movement from the Great Basin (Butler 1981). There is archaeological evidence of continual human occupation, alternating between Bison and Veratic Rockshelters, dating as far back as 11,000 years ago (Butler 1981). Initial work in this rich valley region was begun with an archaeological reconnaissance survey in 1958, which led to the rockshelter excavations during the field seasons of 1960 and 1961 (Swanson 1972).