During 1981 and 1982 the U.S. Geological Survey and the U.S. Bureau of Mimes conducted field investigations to evaluate the mineral resource potential of the Sandia Mountain Wilderness, Bernalillo and Sandoval Counties, New Mexico. This report and map represent only the results of the aeromagnetic compilation from previous publications (U.S. geological Survey, 1975a,b,c). The wilderness encompasses 61 mi² (37,232 acres) within the Cibola National Forest, but the map area is about 145 mi² and includes areas adjacent to the wilderness boundary.

The Sandia Mountains are a part of an eastward-tilted fault block that is about 18 mi long and 8-10 mi wide and that is continuous with the Manzanita-Manzano Mountain fault blocks to the south of Tijeras Canyon (fig. 1). The westward-facing Sandia range front of Precambrian crystalline rocks is capped by about 2,500 ft of Pennsylvanian and Permian limestone, sandstone, and siltstone strata that dip 15°-20° eastward to form the dip slope of the tilted fault block.

About 40-50 percent of the rocks exposed in the Sandia Mountains are of Precambrian age and include an older group of greenstone, metarhyolite, quartzite, and gneiss that is intruded by the Sandia Granite (1,445 m.y.). Paleozoic strata, about 2,500 ft thick, comprise about 30 percent of the outcrop area and form an extensive dip slope on the tilted fault block. Mesozoic strata commonly occupy synclinal basins such as that near Placitas in the Santo Domingo basin. Tertiary strata are represented by the early Tertiary Galisteo Formation and the poorly consolidated basin-f111 sediments of the Santa Fe Group.

The dominant structural element is the east-tilted Sandia fault block, which is bounded on the west by the Pliocene and Miocene Sandia and Rincon-Ranchos range-front faults. These faults have as much as 20,000-28,000 ft of throw. Numerous north-trending faults along the dip slope are considered coeval with the range-front faults and have had an important influence on the localization of barite-fluorite veins. The northeast- and east-northeast-striking Placitas-San Francisco, Tijeras, and Gutierrez faults are principally of Laramide age but probably had numerous periods of movement.

Regional gravity data (Suits and Cordell, 1981) indicate no significant mass distribution anomalies within the study area.