LATE PLEISTOCENE AND HOLOCENE GEOARCHAEOLOGY AND PALEONTOLOGY AT THE SHEEP ROCK SPRING SITE, MONTANA

The Sheep Rock Spring site (24JF292) is a stratified alluvial/colluvial locality with Late Pleistocene paleontological and early to late Holocene archaeological horizons. Located on the flank of Bull Mountain near Golden Sunlight Mine, NE of Whitehall, MT, the site sits in a small valley between Sheep Rock, a prominent bedrock eminence, and a smaller relict tor informally named the "Camel's Hump." Excavations revealed a sloping bouldery diamict representing a landslide from Camel's Hump, overlain in turn by a debris flow, late Pleistocene to early Holocene channel to overbank alluvium, and finally an alluvial/colluvial fan built across the valley in the mid-to-late Holocene. Radiocarbon dates on charcoal and bones in alluvium and colluvium extend back to 10.1 ka, with cultural associations from 9.3 ka. Bones of Pleistocene vertebrates are present in interstitial sediments within the landslide diamict and include bighorn sheep (Ovis canadensis catclawensis), camel (Camelops sp.), horse (Equus sp.) and cheetah (Acinonyx trumani). Radiocarbon dating of these has thus far failed due to presence of contaminants; the bones lie within the zone of fluctuating water table. Regional considerations suggest ice-free conditions ca. 14.5 ka and this fauna is consistent with other late Pleistocene faunas of the intermontane west and plains. The overall geological sequence suggests periglacial fracturing and a rock avalanche from the tor, perhaps assisted by seismicity in this active region; late Pleistocene to early Holocene sustained alluviation with early debris flows; then increasing slopewash and colluviation from local slopes with elevated temperatures and lowered effective vegetative cover (lowered phytostability) by mid-Holocene. In the course of this activity the location of Sheep Rock Creek has been deflected back and forth across its valley, resulting in both lateral and vertical facies complexity.