Industrial mineral site no. 1476, known as "Poison Lake" is a site in Okanogan County, Washington. This site has been associated with magnesium sulfate. A notation found in DGER Bulletin 37 on page 95 says "Mixed salts occur as solid bed 20 ft. thick over area of 20 acres. Total of 820,000 tons of various crystalline salts. Little, if any, crystalline epsomite remains of the original mass, said to have measured 300 by 200 by 25 ft. Analysis of lake-bed", and designates the value as "Intermittent production by Agro Minerals, Inc., Tonasket, Wash".
