Fluvial and lacustrine sediments of great thickness accumulated in the intermountain basins of the western United States during Tertiary time. The Salt Lake group in northern Utah and parts of surrounding states is a conspicuous stratigraphic unit of these basins. The "beds of light color" in Morgan Valley in the Wasatch Mountains of northern Utah were named the "Salt Lake group" by Hayden (1869) because of similar occurrences in Salt Lake Valley and because he reasoned that the succession could be divided into formations. Similar rocks crop out in Ogden Valley, north of Morgan Valley, and in Cache Valley, Utah and Idaho. Cache Valley is bounded by the Wasatch and Malad Ranges to the west and the Bear River Range to the east (Fig. 1). It extends from the divide between Ogden and Cache valleys about 18 miles south of Los an. Utah. to Red Rock Pass. about 19 miles northwest of Preston. Idaho. The Bear River enters Cache Valley northeast of Preston. Idaho. and leaves through the Bear River Narrows west of Logan. Utah. at a point between the northern end of the Wasatch Range and the Malad Range. Red Rock Pass, northwest of Preston, Idaho, was the outlet of Lake Bonneville.