Key sites in the region have helped to build this understanding.

Cooper’s Ferry in west-central Idaho has produced the oldest well-dated evidence of human occupation on the Snake River, with dates extending back beyond 15,000 calibrated years ago and an assemblage that predates the Clovis horizon, featuring stemmed point technology that may represent a precursor or early expression of the Western Stemmed Tradition.

Paisley Caves in south-central Oregon produced Clovis-age coprolites with human DNA alongside Western Stemmed points, establishing that the two traditions were genuinely contemporary in at least some part of the West.

Connley Cave and Fort Rock Cave in the Fort Rock Basin of Oregon contributed additional early dates for stemmed point occupations.