AMS Dates from Four Late Prehistoric Period Rock Art Sites in West Central Montana

Abstract

In 2002, eight pigment samples were collected from three rock art sites in the Big Belt Mountains of west central Montana. Samples from Hellgate Gulch (24BW9), Avalanche Mouth (24BW19), and the Gates of the Mountains (24LC27) were dated using plasma-chemical extraction and accelerator mass spectrometry. The dates were statistically indistinguishable with ages of 11701 ± 45, 1225 ± 50, and 1280 1 ± 50 B.P. When calibrated, these ages range from 650 to 990 cal A.D. This corresponds to the early Late Prehistoric period on the Northwestern Plains. An oxalate accretion sample overlying a painted area at another site, Big Log Gulch (24LCI707), provided a minimum age of 1440 ± 45 B.P. for the rock art present at this site. The dated images at the four sites fit within the Foothills and Eastern Columbia Plateau rock art traditions.