Geologic map of the Agua Fria quadrangle, Santa Fe County, New Mexico
By Ralph R. Shroba, Ren A. Thompson, Scott A. Minor, V.J.S. Grauch, and Theodore R. Brandt
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The geologic map of the Agua Fria quadrangle, Santa Fe County, N. Mex., portrays the geology in the southern part of the Española basin in and near the western part of the city of Santa Fe. Sediments and lava flows exposed in the map area record alluvial, colluvial, and volcanic processes over the past 15–16 million years. The map area includes part of an alluvial piedmont along the western flank of the Sangre de Cristo Mountains and the eastern margin of the Cerros del Rio volcanic field (CDRVF). Sediments include surficial deposits, composed chiefly of stream alluvium, sheetwash deposits, and colluvium, as well as gravel, sand, and finer deposits of the Santa Fe Group. Sediments of the Santa Fe Group (Ancha Formation and the upper coarse unit and the lower unit of the Tesuque Formation) are locally major aquifers in the Santa Fe area. Lava flows and related sediments of the CDRVF include six lava flows of basaltic to andesitic composition, basaltic tephra, and basaltic alluvium. Numerous faults in the map area cut Miocene sediments of the Tesuque Formation. Most strike north–northeast, dip either west or east, and exhibit normal or normal-oblique slip slickenlines. A few faults cut sediments of the Ancha Formation of Pliocene and possibly early Pleistocene age (as young as about 1.5-1.8 million years old). Numerous aeromagnetic lineaments in the map area, which are inferred to be faults, trend subparallel to faults mapped at the surface. Many of these lineaments are not coincident with surface faults, suggesting the presence of other, possibly buried faults.
Posted February 2006
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