About 30 million years ago, uplift of the bordering Temblor and Caliente mountain ranges and movement along the San Andreas and San Juan faults caused the land between them in the Carrizo to subside into a closed basin. Runoff from adjacent slopes collected there and formed a vast lake that gradually filled with soil-forming sediments, leaving Soda Lake as the remnant of this prehistoric sea. This 3,000 acre alkali wetland provides habitat for migratory birds, waterfowl, shorebirds, and brine shrimp. Research suggests that Native Americans used the salts in Soda Lake long before cattle ranches mined the lake for salt licks and preserving meats. Commercial mining occurred intermittently from the 1880s to 1940. Before 1908, the Carrisa Chemical Company spent $60,000 on a processing plant with a capacity of 600 tons per month to recover sodium sulphate, and it also built a narrow-gauge railroad on the lakebed from the north end of Soda Lake to a refining plant on the south shore. Minerals were obtained by digging below the crust into black mud, pumping water into two small sections of the lake to dissolve crude salts, then pumping the brine into two earthen tanks about 80 square feet and 40 inches deep for solar evaporation. The salts were then crushed and washed with mineral oil, dried in centrifuges, sacked, and hauled to McKittrick for distribution.