This report contains four detailed maps depicting the distribution of Quaternary alluvial deposits and their associated geomorphic surfaces in the northern portion of the Verde Valley. Preliminary age estimations based on relative age criteria and soil development characteristics are assigned to each unit. Each map also depicts the distribution of generalized bedrock types in the area. Geologic structures in the bedrock units other than the principal trace of the Verde Fault are not included in these maps. Each map in this report contains a wealth of geological information concerning the effects of Quaternary climatic fluctuations on the evolution of the Verde River, its major tributaries, and adjacent piedmont areas. Evident in these maps is the strong influence of drainage basin and substrate lithology on the evolution of the regional landscape and the persistence of landforms. In addition, the maps contain information relevant to the distribution and character of flood hazards, vegetation assemblages, and potential soil problems. (20 pages; 4 map sheets, map scale 1:24,000)

This report and accompanying maps describe the surficial geology, geomorphology, and geologic hazards of the northern Tucson metropolitan area. The mapping covers the Tucson North and Sabino Canyon 7 1/2’ quadrangles and includes portions of the City of Tucson and unincorporated Pima County (Figure 1). The map area encompasses the northern part of the basin floor, the southern flank of the Santa Catalina Mountains, and the dissected piedmont between them known as the Catalina foothills. Basin floor areas have been thoroughly altered by urban development, and the Catalina foothills have undergone substantial development during the past 30 years or so. The mountains generally are within the Coronado National Forest and are not developed, but some homes have been built on the lower flanks of the mountains up to the forest boundary. This report is intended to enhance our understanding of the recent geologic development of the northern Tucson metropolitan area and to aid in assessing and understanding geologic hazards in this area. This surficial geologic mapping is part of continuing efforts by the AZGS to map the geology of the Phoenix – Tucson urban corridor, and it complements previous mapping efforts in the Tucson area (McKittrick, 1988; Jackson, 1989; Demsey and others, 1993; Field and Pearthree, 1993). We have incorporated recent mapping and description of the geologic framework of the Catalina foothills (Dickinson, 1999) into this map. The report is organized into a brief introduction and explanation of mapping methods, unit descriptions, a summary of the geologic and geomorphic framework of the area, and a discussion of geologic hazards. (28 pages)

Management of flood hazards on piedmonts of the western United States is increasingly important as urban development expands into these areas. In the western United States, the term “piedmont” describes the low-relief, gently sloping plains between mountain ranges and the streams or playas that occupy the lowest portions of the valleys. Distributary, downstream- branching fluvial systems are common in piedmont areas, and all or parts of many of these distributary systems are active alluvial fans. Management of flood hazards on active alluvial fans is particularly challenging because of complex flow patterns, widespread inundation, local high-velocity flow, and the potential for development of new channels during floods. Geologic and geomorphologic analyses provide insights into the fluvial processes on piedmonts and thus can be invaluable in assessing flood hazards (Pearthree, 1989; Baker and others, 1990; Field and Pearthree, 1991; Hjalmarson and Kemna, 1991; Pearthree and others, 1992; Hjalmarson, 1994; Field, 1994a; 1994b; National Research Council, 1996; Field and Pearthree, 1997; Pearthree and others, in press). This field guide provides an overview of investigations of the Tiger Wash distributary drainage system in western Arizona, which experienced an extreme flood in late September, 1997. (34 pages)

This report and maps describe the geology, geomorphology, and geologic hazards in the Three Points quadrangle, on the southwestern fringe of the Tucson metropolitan area in unincorporated Pima County (Figure 1). The map area is located in the transition between the upland, moderately dissected Altar Valley to the south and the broad, undissected basin called Avra Valley to the north. The community of Three Points (also called Robles Junction) lies on the approximate boundary between these two geographic areas. The map includes a nine-mile-long reach of Brawley Wash, which cuts through the map area from southwest to northeast. Brawley Wash heads just south of the U.S. – Mexico border and drains all of Altar and Avra valleys before joining the Santa Cruz River northwest of Tucson. About 60 percent of the Three Points quadrangle consists of the northwestern piedmont of the Sierrita Mountains. The quadrangle also includes a small part of the northwestern piedmont of the Coyote Mountains and the southern fringe of the Roskruge Mountains. The quadrangle is generally undeveloped, and is currently used primarily for grazing. Some low-density suburban development has occurred around the community of Three Points and on the Sierrita and piedmont to the south. Much of the floodplain and terraces of Brawley Wash has been developed for agriculture. The Three Points quadrangle will likely experience much more urban/suburban development in the next few decades. This map and report may be of use in avoiding or mitigating geologic hazards in this area. (21 pages)

This report summarizes the geology and geomorphology of 12 small watersheds in the Peloncillo Mountains, southwestern New Mexico. The study site is located in the central portion of the Malpai Borderlands project area, on the eastern piedmont of the southern Peloncillo Mountains (Figure 1). It consists of an eastward trending ridge with small dissected basins on either side, and is bordered on the north and south by Walnut and Whitmire creeks, respectively. These creeks flow eastward into southern Animas Valley. The U. S. Forest Service has selected 12 watersheds along the ridge (Figure 2) for a paired watershed experiment to compare effects of two burning seasons, spring and summer, on native vegetation, wildlife, surface water flow, slope stability and erosion (G. Gottfried, US Forest Service, pers. comm., October 2000). As part of this experiment, the Forest Service is installing a sediment trap and two different-sized flumes on each study watershed to record and compare sedimentation and surface flows before and after burning. One flume will be located about 50 feet downstream from the sediment trap and will record higher volume flows of up to 57 cubic feet per second (cfs). Another flume will be located 18 feet further downstream and will record lower volume flows of up to 4 cfs (G. Gottfried, US Forest Service, pers. comm., October 2000). A major concern with this study area is that local geology may provide pathways for surface water to infiltrate and flow between study watersheds, causing erroneous runoff results, or to circumnavigate the flumes altogether. Another concern is a potential increase in erosion rates, or decrease of slope stability, after burning. The purpose of this report is to describe the geologic and geomorphic framework of the study area, to delineate surficial deposits to help define potential erosion, and to provide information concerning potential for sub-surface flow between watersheds or under the flumes. Field investigations and mapping were done in November, 2000, and January, 2001. A 1:12,000-scale map showing bedrock and surficial geology is included with this report.