The 86th annual meeting of the Cordilleran Section of the Geological Society of America was held in Tucson, Arizona in March 1990. The occasion provided an opportunity for geologists studying central and southern Arizona and Sonora, Mexico to lead field trips to their study areas. Field guides for 16 of the 18 field trips run in association with this meeting are included in this special paper. Field guides for the two remaining trips may be purchased from the American Geophysical Union. A primary responsibility of the Arizona Geological Survey is to provide information on the geology and mineral resources of Arizona. This special paper was published to offer the public a guide to outstanding and generally accessible geologic features in the Southwest and an explanation of their significance. We believe that a better understanding of the geology and mineral deposits of the Southwest will lead to greater appreciation of their complexity and diversity and to more responsible stewardship of Arizona's land and mineral resources.

In 1981, Phil Anderson and Karl Wirth published a NURE report, 'Uranium potential in Precambrian Conglomerates of the Central Arizona Arch". We are now releasing six of the geologic and geochemical maps compiled during that study. Also provided is the original 550-p NURE report with data that accompanies these maps. BRIEF MAP DESCRIPTIONS FIGURE 2. Central Arizona Arch Study Area. Compilation of mineral Data and Previous geologic studies. Approximate footprint 111.5 W – 110.5 W; 34.50 N – 33.5 N (Base Map – Mesa & Holbrook AMS 2 degree sheets (1:250,000 enlarged to 1:125,000). Includes mining localities and commodity. Annotated with legend. FIGURE 3. Central Arizona Arch Study Area II. Geology of Precambrian Conglomerates. Approximate footprint 111.50 W – 110.50 W; 34.50 N - 33.50 N,. (Base Map – Mesa & Holbrook AMS 2 degree sheets (1:250,000 enlarged to 1:125,000). Includes legend. FIGURE 4. Central Arizona Arch Study Area III. Geochemical Samples & Results. Approximate footprint 111.50 W – 110.50 W; 34.50 N - 33.50 N,. (Base Map – Mesa & Holbrook AMS 2 degree sheets (1:250,000 enlarged to 1:125,000). Includes geochemistry key. FIGURE 5. Mazatzal Wilderness Study Area: Preliminary Geologic Map of Mazatzal Group Outcrops. Approximate footprint 111.625 W – 111.375; 34.25N - 34 N. Base maps: Cypress Butte, North Peak, Mazatzal Peak and Table Mtn. 7.5’ quadrangle. Includes legend. FIGURE 6. Mazatzal Wilderness Study Area: Geochemical Samples and Results. Approximate footprint 111.625 W – 111.375; 34.25N - 34 N. Base maps: Cypress Butte, North Peak, Mazatzal Peak and Table Mtn. 7.5’ quadrangle. Annotated map and Includes geochemical key. FIGURE 32. Central Arizona Arch Study Area: Precambrian Paleogeographic Setting. Approximate footprint 111.50 W – 110.50 W; 34.50 N - 33.50 N,. (Base Map – Mesa & Holbrook AMS 2 degree sheets (1:250,000). Annotated map. FIGURE North Tonto Basin overview– Sketch geologic map with explanation. (not included in NURE study?) FIGURE Tonto Basin Structural Geology Overview - Base Maps: 1:62,500 and 1:24,000 topos; McFadden Peak, Woods Canyon, Young, Payson North, Diamond Point, Promontory Butte, Payson South, Mcdonald Mtn., Diamond Butte, Gisela, Sheep Basin Mtn., Buzzard Roost Mesa, Kayler Butte, Picture Mtn., Copper Mtn. (not included in NURE study?)

County geologic map of Gila County. Map scale 1:375,000. Contour interval is 500 feet.

Arizona has several deposits of subsurface salt (sodium chloride) that are thicker than the Grand Canyon is deep (Peirce, 1981a). These deposits are some of the thickest in the world (Peirce, 1989; Faulds and others, 1995, 1998). Salt in Arizona is solution mined for industrial purposes near Phoenix and used to store liquefied petroleum gas (LPG) near Phoenix and Holbrook. Salt deposits near Phoenix and Kingman are being considered for the storage of natural gas. Several other basins have potential for the discovery and development of significant salt deposits.

The 1:24,000 scale geologic map that is the basis for this report covers part of the central Mazatzal Mountains in the area where the Beeline Highway (State Highway 87) crosses the range (Figure 1). The map area includes all of the Reno Pass 7 ½' Quadrangle, the eastern third of the Lion Mountain 7 ½' Quadrangle, and the western third of the Kayler Butte 7 ½' Quadrangle. Parts of this area have been mapped and studied by several investigators (Figure 2), whereas other areas remain unmapped, in part because Arizona interior chaparral is difficult to pass through and may require crawling under and climbing over for large distances. This map is an attempt to compile and synthesize maps and unit descriptions from these diverse studies. A stratigraphic correlation diagram is included as figure 3.

The Picture Mountain quadrangle is centered on the southwest flank of the Sierra Ancha (see Figure 1). The geology of the area is dominated by the middle Proterozoic Apache Group and the diabase that intrudes it, and some extensive middle Tertiary conglomerates. Elevations range from about 2800 feet in the southwest comer of the map to 6610 feet at Bear Head Mountain.

Windy Hill quadrangle is located in SE part of Tonto Basin and includes bedrock on both sides of the Basin. Bedrock geology is dominated by Middle Proterozoic Apache Group and by overlying lower Paleozoic sandstone and carbonate rocks. Preliminary Bedrock Geologic Map and Cross Sections of the Windy Hill 7.5' Quadrangle, Gila County, Arizona

This report is a brief summary of the geology and mineral resources of the Tonto Basin, prepared in conjunction with a mineral potential report for a proposed land withdrawal in the Theodore Roosevelt Lake area, requested by the Bureau of Reclamation (Federal Register, v.62, No. 232, p63957, Dec. 3, 1997). This report is based on available published literature and recent mapping by geologists from the Arizona Geological Survey.

Three wells drilled in the Tonto Basin have been studied to assist in the interpretation of subsurface geology of the basin. These are the Forest Service Windy Hill Test #1, drilled in 1991, the Sanchez O'Brien Federal 1-4, drilled in 1983, and the Kerber 1 Federal, drilled in 1969. Locations and other information about the wells are included in Table 1.

The Theodore Roosevelt Dam area is located approximately 90 km east of Phoenix on the southwest flank of Tonto Basin (Figure 1). The map area encompasses the southeastern end of the Mazatzal Mountains and the northern Two Bar Ridge area at the northeastern end of the Superstition Mountains. The area was mapped during November, 1997 to April, 1998, as part of a multiyear mapping program directed at producing a geologic map of the Theodore Roosevelt 30' x 60' Quadrangle. A 1 :24,000 scale map is the primary product of this study (Plate 1; Figure 2), and the accompanying report describes rock units and other geologic features and includes modal mineral analyses of granitic rocks that was done in order to classify the granitoids.