Post-Precambrian rocks of this area include only strata of Mississippian and younger ages. Older Paleozoic rocks probably were deposited in west-central New Mexico, but were removed during various errosional cycles prior to Mississippian deposition. Thin remnants of Mississippian limestone occur in the Ladron, Lemitar, and Magdalena Mountains. Pennsylvanian sediments record a complex history of deposition and erosion, as they thin toward the west from almost 3,000 feet in the Ladron Mountains to zero over the buried ancestral Zuni Mountains. Permian evaporite, carbonate, and sandstone thicken southward from less than 1,000 feet in the Zuni Mountains to more than 2,600 feet in parts of Catron County. Triassic and Jurassic sediments also thin in this direction and are absen in southern Catron and adjacent parts of Socorro Counties. Sandstone and shale of Cretaceous age are exposed in large areas. Early Tertiary erosion caused thinning of these rocks toward the south and southwest. Thick sequences of Tertiary sediments and volcanics, rhyolitic to basaltic in composition, underlie considerable areas in Catron and Socorro Counties, and extensive Quaternary basalt flows cover large areas in central Valencia County.

The best possibility for petroleum accumulation appears to be in unconformity traps in the Pennsylvanian east of the late Paleozoic ancestral Zuni uplift. Cretaceous sandstone and Permian carbonate and sandstone are secondary objectives in this and other parts of west-central New Mexico. The possibility of helium accumulation in the upper part of the Permian is an additional incentive for exploration in this area.

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