Abstracts Earth and Environmental Sciences

Hydrogeology of the Sutter Basin, Sacramento Valley, California

by George Curtin

A mound of saline water exists in continental sediments between two fresh water rivers in the Sutter Basin of the Sacramento Valley, California. This saline water has moved from the marine sediments, at depth, upward along the Sutter Basin Fault and then through 2,000 feet of alluvium. The hydraulic head required to move the connate water is supplied by the high topographic position of the Cretaceous sediments carried up by the Sutter Buttes intrusives and exposed at the surface some 250 to 400 feet above the valley floor. Around the Buttes the marine sediments have been flushed with fresh water to depths of over 2,000 feet. The displaced saline connate water has moved south where it intercepts the Sutter Basin Fault. The geologic section consists of about 5,500 feet of Cretaceous and Eocene marine sediments which have been deposited atop the basement complex (the western extension of the Sierra Nevada fault block) and capped by 2,000 feet of post-Eocene alluvium. Chemical analyses of the ground water indicate sodium chloride water is being introduced from depth, and as the rising connate water moves northerly into the orchard area it changes to a calcium-magnesium chloride type water.