Rockshelters in the Bighorn Mountains play a key role in Central Rocky Mountains and northern Plains archaeological research. While many rockshelters have been excavated, no systematic geoarchaeological investigations have considered spatial and temporal variation in physical site formation processes or potential contributions to regional paleoenvironmental records. This study presents stratigraphie, sedimentological, and geochronological (¹⁴C and optically stimulated luminescence) information for 10 rockshelters with deposits dating >30,000 ¹⁴C yr BP to present. Roof fall and eolian sedimentation are common prior to 13,000 ¹⁴C yr BP reflecting cool, dry late Pleistocene conditions. A predominance of hillslope alluvium and roof fall ca. 13,000-10,000 ¹⁴C yr BP indicates a shift towards a moister terminal Pleistocene. Increases in eolian sedimentation punctuated by periodic hillslope alluvium characterized a relatively dry early Holocene ca. 10,000-8000 ¹⁴C yr BP. Stochastic early Holocene precipitation associated with an enhanced North American Monsoon increased floodplain instability. Mixed eolian and hillslope sedimentation continued through the middle Holocene to ca. 6000 ¹⁴C yr BP indicating spatially variable response to climate change where elevation in the Bighorn Mountains moderated aridity in the eastern Bighorn Basin. Hillslope alluvium is dominant after 6000 ¹⁴C yr BP indicating decreased aridity, although periodic late Holocene eolian sedimentation evidences episodic drought.

This study confirms the presence of latest Pleistocene deposits, supporting the argument that relatively low intensity use of rockshelters by Early Paleoindian groups is not due to sampling. Moreover, dry early Holocene conditions inferred from rockshelter stratigraphy likely served as the ecological impetus for the origin of the distinct Foothills-Mountain Paleoindian tradition immediately following the terminal Pleistocene. This study also couples geoarchaeological and zooarchaeological analysis to demonstrate relationships between short-term (i.e., centennial) climate change and human adaptation. A detailed analysis of one rockshelter suggests a ≥100-year lag time existed between late Holocene climate change and human subsistence response, i.e., expanding diet breadth and intensively processing animal carcasses. This study lays the groundwork for future environmental archaeological research in the Bighorn Mountains and other Central Rocky Mountains ranges.