The Sierra Blanca area is on the northern margin of the Chihuahua Tectonic Belt and is a massive complex of volcanic rocks including pyroclastic materials, lava flows, and intrusions. Round Top Mountain is a surface-exposed rhyolite intrusion that was created from molten liquid rock pushing up from beneath the earth's surface. The top layer of sedimentary rock that makes up the mountain has been eroded over time, exposing the rhyolite formation. It also contains quantities of Del Rio Clay and Finlay limestone as well as deposits of uranium and lithium. The area contains scrub brush and grasses that are supported by the mountain's sandy loams and clay.