From introduction: This is one of a series of detailed studies of the antimony deposits of Mexico, which were investigated by the United States Geological Survey and the Instituto de Geologia de Mexico. The investigation was part of a cooperative program sponsored by the Interdepartmental Committee for Scientific and Cultural Cooperation, under the auspices of the Department of State.

From abstract: The Santa Clara coal district is 7 to 10 kilometers west of Tonichi, a small town on the Rio Yaqui, in southeastern Sonora, Mexico. Tonichi was the terminus of a branch railroad from Corral until May 1945, when the end of the line was removed. The coal deposits were developed by the Southern Pacific Railroad from the 1890's until about 1911, when the mines were abandoned, partly because the coal was found unsuitable for use in locomotives. Other coal deposits, near Los Bronces and San Javier, west of the Santa Clara district, were mined for a number of years to provide coal for a silver smelter at San Javier which was abandoned sometime during the 1920's. Since 1942 the Santa Clara deposits have been reopened; through 1945 about 50,000 tons of coal had been shipped, at first to the Boleo copper smelter at Santa Rosalia, Baja California, and more recently to Guadalajara, Jalisco, for the manufacture of calcium carbide.