This report was prepared for the United States Air Force under an agreement t o compile and summarize available information on the geology, minerals and energy resources of the Luke Air Force Range. The primary focus of this investigation is to compile a general inventory of mineral production and mineral resources activity on the Luke Air Force Range (LAFR) . LAFR i s a wedge-shaped land area o f 2,673,156 acres lying in the southwestern corner o f Arizona and spanning portions o f Yuma, Maricopa and Pima Counties. The LAFR complex extends east-west between the communities of Ajo and Yuma, Arizona. Its northern boundary is formed by the Gila River Valley, a mainline of the Southern Pacific Railroad, and U.S. Interstate Highway 8. Limiting its southern extent is the International Boundary between the United States and Mexico. The eastern boundary is formed, in Maricopa County, by the Vekol Valley and the Papago Indian Reservation and, in Pima County, by the town of Ajo and the Organ Pipe Cactus National Monument. The Colorado River Valley forms its western boundary (Figure 1 ). LAFR has a maximum north-south dimension o f approximately 60 miles and an east-west dimension of approximately 130 miles. The LAFR complex is shown on parts, or all, of 44 United States Geological Survey quadrangle maps (Figure 2). Included within the boundaries of LAFR are the 825,440 acres comprising the Cabeza Prieta Game Range (Figure 1). The game range i s administrated by the United States Fish and Wildlife Service.

In 2011, the Arizona Wilderness Coalition, Sonoran Institute, and The Wilderness Society proposed that the Federal Government designate approximately 1170 square miles (~750,000 acres) of Arizona public lands as Wilderness Area, National Conservation Area, and Special Management Area (Marlow and Richins, 2012). These lands are located primarily west of Phoenix in the low deserts of western Arizona. Enactment of this “Sonoran Desert Heritage” proposal would prevent mining and quarrying on these lands, and would prohibit or impede exploration activity such as drilling and geophysical surveying. This report is an evaluation of the mineral resource potential of these lands, but is limited to the following types of deposits: (1) sand and gravel (aggregates), which are used for concrete and asphalt, (2) porphyry copper deposits, which are a specific type of large copper deposit that is common in Arizona (these deposits may yield large amounts of byproduct molybdenum, silver, and gold), (3) gold deposits in veins, some of which contain substantial silver, and (4) manganese deposits, which are present over a large area in western Arizona but, historically, have been too low grade for mining. The geology of the lands included within the Sonoran Desert Heritage proposal is complex, and varies greatly from range to range. Geologic mapping of almost the entire area, done by Arizona Geological Survey geologists under the joint State-Federal STATEMAP and COGEOMAP programs over the past 30 years, allows informed evaluation of mineral resource potential. This report identifies areas that have high potential for future aggregate production, and areas considered favorable for future discovery of porphyry copper deposits, precious-metal vein deposits, and manganese deposits. One area encompassed by the Sonoran Desert Heritage proposal, which includes the Harquahala and Big Horn Mountains, is identified as having high potential for all of these deposit types. Other metallic mineral commodities such as uranium, iron, and rare-earth elements, and industrial minerals such as clay and zeolite, were not evaluated. This report also includes a brief review of USGS designations of proposed SDH lands as “permissive” and “not permissive” for future discovery of several mineral commodities. Finally, it should be noted that evaluations of potential for undiscovered mineral deposits are inherently speculative, and are complicated by the fact that new technologies for mining and quarrying, changing economic conditions, and changes in commodity demand may result in some uneconomic deposits becoming economic, or in previously uninteresting deposits becoming targets for exploration and mining. As a result, removal of even unattractive lands from mining and quarrying can eventually have adverse economic consequences.

Persons traveling over Arizona highways encounter an ever changing variety of scenery, geologic features, climate, vegetation, wild life, and conditions for human habitation and industry. All of these have a close relationship to the physiography and geology of the particular area. In passing through the region, the viewer of the landscape, particularly if a stranger, may want to know more about what he is seeing and what has happened. This road guide to a part of the southwestern Arizona desert is designed to answer at least some of such questions, by keying brief descriptions to points of interest in a sequential manner. The amount that a traveler can see depends largely on the speed of his transit. This guidebook is planned primarily for those who wish to take time to observe the general geologic setting and physiographic features, and to understand their effects on life in the region. effects on life in the region. The text, illustrations, and appendices are designed to provide a thumbnail sketch of what is there and what has, and is taking place. To those who wish to know more, the selected bibliography furnishes numerous references that may be explored. 80 p.

The diversity of alluvial fan and pediment ages and the pristine Sonoran desert vegetation of the Table Top Mountains make this region ideally suited to study relationships between geomorphic surfaces, soil development, and vegetation distribution. The Table Top Mountains and flanking piedmonts, located about 30 km (20 mi) southwest of Casa Grande and about 50 km (30 miles) east-southeast of Gila Bend in south-central Arizona, lie mostly within the Table Top Wilderness Area, administered by the Bureau of Land Management (Fig. 1). The range is dominated by the mesa-like Table Top Mountain (1333 m, 4374 ft elevation) and is surrounded by smaller hills and extensive alluvial deposits of varying ages. This study describes the surficial geology, soils, and vegetation patterns on the piedmonts flanking the mountain mass.

The little Horn Mountains 30' x 60' quadrangle is situated in the Sonoran Desert section of the Basin and Range Province in southwestern Arizona. This map depicts the alluvial deposits that compose the piedmonts (broad,gently sloping valley sides) and basins (valley floors).

This map depicts the general ages and distribution of Quaternary alluvium within the Phoenix South 30' x 60' quadrangle. The quadrangle is situated south and wear of Phoenix, in the Sonoran Desert section of the Basin and Range Province. Map scale 1:100,000.

The Phoenix North 30' x 60' quadrangle covers an area in south-central Arizona that straddles the boundary between the Sonoran Desert and Mexican Highland sections of the Basin and Range Province. Map scale 1:100,000.

The area within the Salome 30 x 60 minute quadrangle is part of the Sonoran Desert within Southern Basin and Range physiographic province. Landforms and geomorphic relationships in this area are products of several independent controlling variables, and such, may serve as analogies for similar mountain/basin settings in adjacent areas of the southwestern U.S. One map sheet, 1:100,000 map scale.

On a clear day the rugged crest of Four Peaks is visible from Phoenix, 50 km to the east-northeast (see figures I and 2). It is one of the highest, most rugged areas in central Arizona. Four Peaks forms part of the high ridge that forms the backbone of the southern Mazatzal Mountains. The Four Peaks quadrangle ranges in elevation from about 2400 feet along Bumblebee Creek in the northeast comer of the map up to 7657 feet at Brown's Peak. Most of the region is extremely rugged and difficult to access. The Four Peaks Road, which branches off State Route 87 at Sugarloaf Mountain (west of the map area), is a good 2-wheel-drive dirt road. The Four Peaks Road becomes the El Oso Road on the east side of the high divide, which is also passable with a 2-wheel drive vehicle. On the east side of the range the road to Three Bar Cabin is also 2-wheel-drive accessible, but the road to Big Oak Flat is very rocky and narrow. The ridge road branching northward from the El Oso Road north to Big Pine Flat is also good, though about 1 mile farther north of Big Pine Flat it becomes rough even for a 4-wheel-drive vehicle. The quadrangle covers a wide range of elevations and bio-zones. On the southwest and northeast comers of the region below about 4000 feet Sonoran Desert vegetation dominates, and includes plants such as saguaro, palo verde, cholla and prickly pear cactus, among others. Above about 4000 feet Sonoran Desert vegetation gives way to dense chaparral vegetation including scrub oak, manzanita, desert mahogany, sumac, and others. The thick chaparral blankets the landscape and creates a nearly impenetrable, dense thicket. This was a major obstacle to detailed mapping in the higher elevations. Fortunately, (or unfortunately) the 1996 Lone Fire that originated near Pigeon Spring burned most of the thick chaparral from the Brushy Basin southward to beyond the southern boundary of the map. In many places dense, ghostly woodlands remained, composed of the charred skeletons of trees and shrubs. Mapping for this project was carried out mostly during May 1997, May 1998, and April-May 1999, during which time I observed the rapid regrowth of the vegetation. Conifer forests grow on a few of the north-facing slopes near Four Peaks and Buckhorn Mountain. During this study most of the trees in these patches of forest were burned. One report and one map sheet, 1:24,000 map scale.

The Arizona Basin and Range Province consists of broad alluvial valleys that separate low but rugged mountain ranges. The broad expanses of dry alluvial deposits and ephemeral streams that characterize the basin areas belie their importance as water sources and their geologic complexity. These basins are geologically interesting as the record of late Cenozoic deformation in southwestern North America. They are economically interesting because of contained salt, anhydrite, manganese, uranium, clay, and zeolite resources, as well as the potential for metallic mineral deposits concealed beneath their sedimentary fill. The alluvial basins contain reservoirs of groundwater that are a vital resource for human occupants. An accurate geologic framework model of these basins is fundamental to scientific understanding of geologically recent continental tectonics, and to the discovery and managed development of the resources contained in the basins. This report provides a snapshot of current understanding of the subsurface geometry of the boundaries of Tertiary basin fill, which is a major component of the necessary geologic framework model.