Prior to the breakup of the Precambrian supercontinent and the formation of the modern Permian Basin geometry, shallow marine sedimentation onto the ancestral Tobosa Basin characterized the passive margin, shallow marine environment. The Tobosa Basin also contains basement rock that dates back to 1330 million years ago (mya), and that is still visible in the present-day Guadalupe Mountains. The basement rock contains biotite-quartz granite, discovered at a depth of . In the nearby Apache and Glass Mountains, the basement rock is made of metamorphosed sandstone and Precambrian-aged granite. The entire area is also underlain by layered mafic rocks, which are thought to be a part of Pecos Mafic Igneous Suite, and extends into the southern US. It has been dated to 1163 mya.