Geology of Souse Springs quadrangle, New Mexico

The Souse Springs 71/2 minute quadrangle in northwestern Dona Ana County, New Mexico, includes the major part of the Sierra de las Uvas. Broadly domed and faulted volcanic rocks and interbedded clastic sedimentary rocks of middle Tertiary age are unconformably overlain by late Tertiary and Quaternary clastic sedimentary rocks. Only along the eastern side of the quadrangle are older rocks exposed by uplift, westward tilting and erosion.Oldest rocks exposed in the quadrangle are the upper part of the Palm Park Formation (probably Eocene) unconformably overlain by the Bell Top Formation (Oligocene) which is subdivided into 6 ash-flow tuff units, a basalt flow, and 2 sedimentary units. Flows of Uvas Basaltic Andesite (Miocene) interfinger with the upper sedimentary member. Thickness and number of flows in the Uvas decrease radially away from the crest of the Sierra de las Uvas. The upper part of the Bell Top and the Uvas correlate with the lower half of the Thurman Formation to the northeast. Graben-fill fanglomerates and interbedded, reddish, basin-floor clastics, derived mainly from the Sierra de las Uvas, comprise the Rincon Valley Formation (Miocene? and Pliocene) which unconformably overlies the Uvas flows. The Rincon Valley Formation is, in turn, unconformably overlain by the Camp Rice Formation (Pleistocene). The Camp Rice is composed of fanglomerates, piedmont gravels, and finer basin facies, that overlap or grade in adjacent areas to fluvial sandstones deposited by the ancestral Rio Grande.Several source areas for the Uvas Basaltic Andesite occurring in the quadrangle are located in complex, faulted grabens axial to the Sierra de las Uvas Dome. Source areas for several members of the Bell Top were probably in the Cedar Hills, southeast of the quadrangle. Late Tertiary faulting uplifted the Sierra de las Uvas range and resulted in tilting of the Uvas Dome to the northwest.