Industrial mineral site no. 596, known as "Langdon" is a site in San Juan County, Washington. This site has been associated with limestone and marble. A notation found in DGER Bulletin 37 on page 53 says "Rises from water's edge in a 75-ft. bluff and is exposed laterally for 200 ft", and designates the value as "Formerly quarried and shipped to Tacoma smelter. Considerable stone remains".