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Production of other metallic minerals including zinc, lead, copper, silver, and gold has been almost entirely from the San Juan Moun- tains in the Si1verton area of San Juan County, Colorado. Sand and gravel produced at pits throughout the basin area are used mainly for construction purposes such as aggregates for concrete, mortar and asphalt, and as road base material. The coal resources of the basin are located mainly in the Mesa Verde group of Upper Cretaceous Age which is at or within 3,000 feet of the surface around the margins of the San Juan structural basin in New Mexico and Colorado. A total of 9,646 million tons of bituminous '" coal is estimated to have been originally present in the Colorado por- tion of the basin. In New Mexico 4,085 million tons of bituminous coal and 28,414 million tons of sub-bituminous coal are estimated to have been originally present. In Colorado and Utah, additional coal resources are present as thin beds in the Dakota Formation, but no firm estimates of the quantities present are available. At present coal production in the basin is relatively low. Other potentially valuable but as yet generally uneva1uated mineral resources of.the San Juan Basin include gypsum, salt (halite), and potash deposits. Some of the gypsum deposits lie at or near the ground surface, but the salt and potash deposits lie at depths of several hundred feet or more. LAND RESOURCES Soils The General Soil Map locates soils with similar characteristics and suitability within the basin. (General Soils Map follows page III-10). Broad characteristics and relationships can then be used to interpret the potential of soils for agricultural, recreational, commercial, and industrial uses. Problems of erosion, sediment yield, land use, and future development are interrelated with soils and their distri- bution. The General Soils Map was prepared by delineating 28 mapping units' that differ from each other in the kinds of soil that are present. Soils in each mapping unit form patterns that are repeated from place-to-p1ace. Mapping units were defined and described according . to requirements imposed by the map scale and criteria from the Com- prehensive System of Soil Classification adopted in January 1965. Soil mapping 'units were placed in six major groups for purposes of broad interpretation. Five of the groups are distinguished by their climates and one is set apart by the fact that it consists of land types and shallow soils. Acreage distribution of the soil mapping units and groups along with percent that each occupies is given in Table 111-1. Dominant characteristics of each mapping unit are given in Table 111-2. II 1-1 0