The Davis Mountains are an erosional remnant of a volcanic field that probably covered 5 to 10 times their present areal extent of approximately 2,000 square miles. Many previous workers believed that much of the extrusive material in nearby parts of western Trans-Pecos Texas was erupted from the central Davis Mountains (Colton, 1957, p. 76; Lewis, 1949, p. 89; McAnulty, 1955, p. 54<3; Zabriskie, 1951, p. 36).