Test excavations at six sites on the North Fork of the Mokelumne River ranging in elevation from 4000 to 8000 feet reveal a 2500+ year sequence divided into three periods on the basis of seriation of flaked stone raw materials, radiocarbon dating, obsidian hydration, and typological comparison. The following periods have been defined:
Blue Lakes Phase (ca. 2500 BP? - 1500 BP)
Mokelumne Phase (ca. 1500 BP - 750 BP)
Amador Phase (ca. 750 BP - 150 BP)
These phases correlate with changes in interaction spheres and proposed climatic changes. A possible divergence in the sequence between the upper elevations and middle elevations suggests population movements generally consistent with Moratto's (1984) model.