HORSESHOE CAVE: GEOARCHAEOLOGY, CLIMATE CHANGE, AND HUMAN OCCUPATION

Located south of Ashland, Montana, Horseshoe Cave contains evidence of Late Prehistoric Period and possibly earlier occupation and use. Geoarchaeological investigations of this sandstone cave in 2010 and 2011 indicate the cave forming process appears to have been initiated tens of thousands of years ago. The process of cave formation has now largely ceased and the majority of materials currently being deposited on the cave floor represent the grain-by-grain disintegration of the sandstone cave walls and the deposition of fine grained clastic materials blown into the cave.

The analysis of a 1.35 m column of cave floor sediment that spans some 2,000+ years indicates a climatic history that includes at least four periods of warm and dry conditions. These warm and dry periods are delineated by an increased percentage of fine-grained sediment. When the distribution of these arid patterns is overlain on profiles containing cultural features (e.g. hearths) it became evident that none of the cultural features coincide with the dry intervals. This is an association that strongly suggests the area immediately surrounding Horseshoe Cave was not as favorable a living environment as might be found along the more mesic drainage bottoms of the region.