The Potrillo volcanic field has two important xenolith localities that are Kilbourne Hole and Potrillo maar where mantle peridotites, feldspathic granulites and kaersutite occur. Alkali feldspar, olivine and basalt were erupted during the middle and late quaternary. Rock samples collected in the northern part of the pyroclastic deposit of the Potrillo maar, and lava associated with a cinder cone yielded potassium-argon ages, approximately 1.29 and 1.18 million years. The magmatism is entirely basaltic forming scattered scoria cones. Several short lava flows were originated from each cone. There is a diverse rock types beneath the Potrillo volcanics, the range is from Proterozoic granites through a Phanerozoic sedimentary succession to basalt-andesite volcanics of the southern fringes of the Sierra de las Uvas volcanic field. The Potrillo area is generally classified as part of the southern Rio Grande rift and shows the Cenozoic tectonic evolution of that structure.