The Plomosa Mining District's Mineralization is very varied: (1) Major gold placer deposits in washes from erosion of numerous quartz veins and veinlets in metamorphic rocks; (2) Spotty, partly oxidized copper and gold mineralization with minor lead and zinc, and with quartz, and iron and manganese oxides in irregular fault and fracture veins in metamorphosed Mesozoic sediments, probably Cretaceous shale, sandstone, conglomerate, and limestone; Precambrian metamorphics, and Cretaceous or Tertiary volcanics, with intrusions of Laramide diorite and granite; (3) Manganese oxides in irregular, lenticular bodies and veinlets with variable amounts of iron oxides, calcite, barite, gypsum, and traces of beryllium along fracture and breccia zones in Cretaceous or Tertiary andesitic volcanics; (4) Barite and fluorite in veins along faults and fractures in Cretaceous or Tertiary volcanic flows and agglomerates; (5) Spotty pods and stringers of copper, lead, and zinc minerals with silver and minor gold, and with associated iron and manganese, in faulted Paleozoic limestone blocks and in irregular veins in Cretaceous or tertiary andesite volcanics cut by Laramide quartz monzonite intrusives; (6) Gold and silver ores in irregular veins along fractures and fault zones associated with quartz stringers and Laramide diorite and granite porphyry dikes in Mesozoic schist; (7) Sporadic scheelite in quartz veinlets in carcareous Mesozoic schist close to Laramide granitic intrusives; (8) Irregular, impure iron oxides, usually associated with manganese, in contact metamorphic deposits in Paleozoic limestone beds close to intrusives; (9) Bentonite clay in probable lake bed sediments; and (10) Minor chrysoprase in stringers in rhyolite.

Workings include numerous scattered small mines and prospects in the northern and southern parts of the district. Deposits and placers have been known and worked intermittently since at least the early 1860's. Estimated and recorded production of base and precious metals from lode mines would be some 26,000 tons of ore containing about 526 tons of copper, 344 tons of lead, 65 tons of zinc, 7,000 oz. of gold, and 127,400 oz. of silver. Placer production of gold would be about 18,000 oz. with 1,800 oz. of silver. Some 9,000 long tons of low-grade manganese ore, 500 tons of iron ore, 2,700 tons of barite ore, 1 ton of tungsten concentrates, and a small amount of bentonitic clay also have been produced. Some chrysoprase has been mined and sold for gem material.