The Palo Verde Mountains are located in the northeastern portion of Imperial County with the McCoy Mountains to the north and the Colorado River to the east. The Palo Verde Range trends northwest-southeast and is approximately 10 miles in length. Approximately 6000 feet of Tertiary volcanic rocks, highly variable in composition, predominate in the area. These sequences include andesites, dacites and tuff breccias. In the vicinity of Palo Verde Peak the younger volcanic rocks overlie the older volcanic rocks with a steep angular unconformity, both units having been strongly tilted. Limestone of Pliocene(?) age, unconformably above the principal volcanic rock units in the southeastern and eastern portions of the area. The area contains a network of faults none of which have more than 30 feet of displacement. Intense fracturing of the younger volcanics in the northern portions of the area is the major structural control relating to the hydrothermal manganese deposits. At least two periods of deformation affected the two Tertiary volcanic sequences. Sequences of limestone and shale with thicknesses on the order of about 75 to 100 feet, were deposited in a shallow marine extention of the Gulf of California.