Abstract Big Pumice is a roadcut alongside U.S. Highway 395 at theeast base of the Sierra Nevada in Mono County, east-central California. The site lies within the NW1/4 of sec. 34, T.4S., R.30E.of Casa Diablo, 15' quadrangle, at 118°39'W Long., 37°33'ELat. It is on the north side of an east-west highway reach, 1.2 mi (2 km) east of Tom's Place, 0.1 mi (0.2 km) east of the crossing ofRock Creek, and 22.8 mi(38 km) by highway northwest of the city of Bishop (Fig. 1).

Oxygen- and hydrogen-isotope analyses of ice cores from a hole drilled 2,164 m through the Antarctic Ice Sheet suggest that the Wisconsin cold interval began about 75,000 yrs B.P., reached its climax about 17,000 yrs B.P., and terminated about 11,000 yrs B.P.