In Cooperation with the Southern Sierra Archaeological Society

U.S. Geological Survey
Scientific Investigations Report 2008-5210
version 1.0

Origin of Meter-Size Granite Basins in the Southern Sierra Nevada, California

By James G. Moore, Mary A. Gorden, Joel E. Robinson, and Barry C. Moring


Photo of Karen measuring basin-water depth with a stick
Rainwater pond in granite basin at Quail Flat site. Water is 110 cm in diameter and 20 cm deep; upper white rim is 148 cm in diameter.


Meter-size granite basins are found in a 180-km belt extending south from the South Fork of the Kings River to Lake Isabella on the west slope of the southern Sierra Nevada, California. Their origin has long been debated. A total of 1,033 basins have been inventoried at 221 sites. The basins occur on bedrock granitic outcrops at a median elevation of 1,950 m. Median basin diameter among 30 of the basin sites varies from 89 to 170 cm, median depth is 12 to 63 cm. Eighty percent of the basin sites also contain smaller bedrock mortars (~1-2 liters in capacity) of the type used by Native Americans (American Indians) to grind acorns. Features that suggest a manmade origin for the basins are: restricted size, shape, and elevation range; common association with Indian middens and grinding mortars; a south- and west-facing aspect; presence of differing shapes in distinct localities; and location in a food-rich belt with pleasant summer weather. Volcanic ash (erupted A.D. 1240±60) in the bottom of several of the basins indicates that they were used shortly before ~760 years ago but not thereafter. Experiments suggest that campfires built on the granite will weaken the bedrock and expedite excavation of the basins. The primary use of the basins was apparently in preparing food, including acorns and pine nuts. The basins are among the largest and most permanent artifacts remaining from the California Indian civilization.

Download this report as a 22-page PDF file (sir2008-5210.pdf; 10.9 MB)

Also of interest

CAL FIRE Archaeology Program -- other reports.

For questions about this report, contact Jim Moore.

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