Site 45-DO-273 is on the south bank of the Columbia River (River Mile 561), near the Okanogan Highland-Columbia Plateau boundary, in an Upper Sonoran life zone. The University of Washington excavated 158.6 cubic meters in 1979 for the U.S. Army Corps of Engineers, Seattle District, as part of a mitigation program for a 10-foot pool raise at the Chief Joseph Dam Project. Systematic aligned random sampling with 1 x 1 x 0.1-meter units of record in 1 x 2 or 2 x 2-meter cells disclosed three prehistoric occuptions on an alluvial fan built onto an early point bar deposit, interbedded with overbank sediments. The two carbon dates obtained are unreliable, several serrated lanceolate projectile points suggest that the first occupation occurred more than 5,500 years ago. The second, more intensive occupation probably occurred about 4,500 years ago. Both of these early occupations fall within the Kartar Phase. The third occupation, in the Coyote Creek Phase, probably took place between 1,500 and 1,000 years ago. The occupations show little change in more than 4,500 years; all are lithic and bone concentrations with microblade technology and lithic stations. The earlier two occupations yielded mussel shell fragments, which are lacking in the later two. No earth ovens or hearths were found. (Author).