Major sedimentary basins in this, the eastern part of the Basin-and-Range province, are the Orogrande and Pedregosa basins of Mississippian, Pennsylvanian, and Wolfcampian age, the San Mateo and Lucero basins of Pennsylvanian age, the Carrizozo and Quemado-Cuchillo evaporite basins of Leonardian age, the Early Cretaceous basin near the Hatchet Mountains, and the continental basins containing much volcanic debris of Late Cretaceous age in central Sierra County and near Steeple Rock. Numerous Cenozoic intermontane grabens occur in the region, including the southern part of a long north-south string of interconnected grabens now followed by the Rio Grande and called the Rio Grande structural depression. Sediments filling the Cenozoic basins are mainly of Miocene, Pliocene, and Pleistocene ages.
Pre-Devonian strata, the Cambrian-Ordovician Bliss Sandstone, the Ordovician El Paso Limestone and Montoya Dolomite, and the Silurian Fusselman Dolomite, thin northward and westward mostly because of periodic erosion but the thinning is partly depositional. The Devonian shaly beds are relatively uniform in thickness, although marking the first large-scale influx of clay and silt. As with all older Paleozoic sediments, they appear to have been deposited in shallow epicontinental seas.
The Pedregosa basin was autogeosynclinal, receiving thick deposits of Middle Mississippian crinoidal limestones, Late Mississippian arenaceous calcarenites, Pennsylvanian limestones, and Wolfcampian interbeds of limestone, black shale, and redbeds. The Orogrande basin began as a poorly defined autogeosyncline in which siliceous Middle Mississippian limestones were deposited, then became zeugogeosynclinal during late Pennsylvanian time as detritus was swept westward from the Pedernal landmass, and during Wolfcampian time was filled by limestone and shale that grade northward into redbeds. The San Mateo and Lucero basins were small autogeosynclines that connected the Pennsylvanian seas northward with the San Juan and Paradox basins.
Source beds and possible petroleum reservoir rocks occur in the Paleozoic and Mesozoic sequences. The reservoir beds include porous sandstone, bioclastic calcarenite, dolomite, reef masses, porous lenses beneath truncating unconformities or amid intertongued redbeds and marine limestones.