The Granite Basin laccolith is located in the Mescal Mountains of the San Carlos Indian Reservation, 15 miles ENE of Kearny, Arizona. According to Willden (1964), the feldspar-mica porphyry intruded the Naco Limestone about 62 Ma. Locally, the Pennsylvanian Naco strikes northwesterly and dips about 25 to 30 degrees to the southwest. At the southeastern end of the laccolith, the Naco Limestone is nearly vertical and strikes to the northeast.