Fifty Years of Wyoming Trona Mining

Abstract The world's largest known resource of natural sodium carbonate is found in 22 beds within the Wilkins Peak member of the Eocene Green River Formation in the Green River Basin of southwestern Wyoming. A recent report by the U. S. Geological Survey estimates that the total resource is 127 billion tons of trona and mixed trona and halite in beds 4 feet or more thick. The resource formed as bedded evaporites precipitated from concentrated brines in the Eocene Lake Gosiute during near-dry or dry conditions. The Wilkins Peak member was deposited during a closed-lake-basin stage of Lake Gosiute. Trona was accidentally discovered in the basin in 1938 when it was identified in a core from the Westvaco #1 oil well, about 25 miles west of Green River. Trona mining began in 1947, and has continued to the present. Recent increases in export markets for soda ash, the primary refined product, have enabled the industry to expand and construct additional capacity. A record 18.2 million short tons of trona were mined in 1995. Although production declined to 17.5 million short tons in 1996, another record of nearly 19 million tons of trona mined should be set in 1997. Increasing export markets, and soft to steady soda ash prices are projected for the next five years.