ARIZONA

The Agua Dulce Mountains and surrounding ranges all lay within the Basin and Range Province of North America. The Basin and Range Province comprises the southern third of the state of Arizona, plus its western edge. It is characterized by linear mountain ranges that mostly trend north-south or northwest-southeast. The mountain chains are separated from each other by downthrown, alluvium-filled basins. Starting from the Tinaja Altas Pass and running eastward to the Agua Dulce Mountains, the Camino del Diablo more or less parallels the Mexican border through nearly 50 miles of mountains and deserts. The mountain ranges in this area all trend northwest-southeast and are predominantly composed of Mesozoic igneous and metamorphic rocks. The metamorphic rocks consist of gneisses, schists, and phyllites. The schists and phyllites are derived from Mesozoic-age sedimentary rocks. The igneous intrusions are silicic, ranging in composition from granite to quartz diorite.

The rock types described above dominate this part of the Basin and Range Province, an area that includes the Gila Mountains, Tinaja Altas Mountains, Cabeza Prieta Mountains, Tule Mountains, Copper Mountains, Sierra Pinta Mountains, Mohawk Mountains, Granite Mountains, and Agua Dulce Mountains. A few Quaternary lava flows occur in the area; the two largest occur in the Cabeza Prieta Mountains and in the Tule Desert. The Tule Desert flow is known as the Pinacate Lava Field; it harbors several cinder cones and is a classic "malpais". All of these Quaternary lava flows are basaltic in composition.

The Agua Dulce Mountains themselves consist almost entirely of Mesozoic-age gneisses. A small exposure of Quaternary basalt lies just south of Papago Well; a few smaller exposures lie scattered to the northwest of Papago Well. Nevertheless, schists, phyllites, and gneisses form the bedrock in the area east of the Pinacate Lava Field and comprise the rugged hills and mountains for nearly 10 miles in any direction.

As previously stated, this part of the Basin and Range Province is weakly mineralized; therefore very few major strikes have been made in the area. But the Fortuna Mine serves as an example of how a major deposit can be overlooked for years. Prospectors should probably concentrate on the rugged country east of Cabeza Prieta (Black Head Mountain). At least one account of the story has the vein partially covered by windblown sand on the southern flank of the peak. Metal-detectors may therefore be of some use in the search. Rich gold-bearing float has been found in this part of southwest Arizona for many years. Careful mapping of any similar discoveries of iron-stained quartz may reveal the source of the gold-bearing float. In any case, it appears that the famous landmark known as Cabeza Prieta will be clearly visible from the lost vein.

Prospectors should realize that much of the Camino del Diablo lies within the Barry M. Goldwater Air Force Range and the Cabeza Prieta National Wildlife Refuge. A permit is required to enter both areas. Permits for entry to the Barry M. Goldwater Range are available from the Marine Corps Air Station, Range Management Department, Yuma, Arizona. Permits for entry to the Cabeza Prieta National Wildlife Refuge are available from the U. S. Fish and Wildlife Service, Ajo, Arizona.