The Santa Cruz Valley National Heritage Area (Figure) covers a wide swath of historic and productive porphyry copper mining in southern Arizona, and mining has long been an important of the history of this region. Our newest Open-File Report, Preliminary evaluation of mineral resources of the Santa Cruz Valley National Heritage Area, Arizona, provides a brief assessment of the mineral resources of the roughly 3,600 square miles (9,378 square kilometers; 2,304,000 acres) of those portions of Pima and Santa Cruz Counties encompassed by the Santa Cruz Valley National Heritage Area. Mineral assessment is largely confined to metallic minerals - copper, gold, silver, lead, zinc and molybdenum extracted from the 20 metallic mineral districts within the heritage area which includes hundreds of mines. Aggregate resources, the building blocks of human society, are also an important component of the mineral resources of the Santa Cruz Valley area.

Lateral bank erosion and channel instability along the ephemeral streams of the Rillito Creek system have posed greater hazards to the Tucson metropolitan area than has overbank flooding. The historical behavior of this alluvial stream system has been investigated to document and evaluate past channel variability, determine potential sites of bank erosion and lateral channel migration, and suggest flood-plain management alternatives to Federal regulations currently applied to semiarid regions. Rillito Creek and its main tributaries, Pantano Wash and Tanque Verde Creek, were mapped from Houghton Road to the mouth of Rillito Creek using aerial photographs taken between 1941 and 1983. These maps, in conjunction with streamflow and channel oomposition data, detail channel change within this stream system.

Geologic map of Pima and Santa Cruz Counties in southeastern Arizona. Map scale 1:375,000.

Extreme flooding in Arizona during the winter of 1993 resulted from a nearly optimal combination of flood-enhancing factors involving hydroclimatology, hydrometeorology and physiography. The flooding which occurred throughout January and February resulted from record precipitation due to a high frequency of winter frontal passages. These fronts were steered across the state by an exceptionally active storm track, located unusually far south. The number of individual storms that entered the region and the relative position of each storm track in relation to previous storms was reflected in a complex spatial and temporal distribution of flood peaks. An analysis of the hydroclimatic context of these floods supports a general conclusion that in Arizona, front-generated winter precipitation is the cause of the most extreme floods in large watersheds, even in basins that tend to experience their greatest frequency of flooding from other types of storms. A comparison of the 1993 floods with gaged, historical, and paleoflood data from Arizona indicates that although many individual flood peaks were quite large, they were within the range of documented extreme flooding over the past 1000+ years.

Geologic maps have traditionally emphasized bedrock rather than unconsolidated sediments, the latter usually being lumped into the generic category of "Tertiary and/or Quaternary alluvium". This tradition has left many areas, especially those within the Basin and Range physiographic province, incompletely mapped. Recently, however, there have been systematic efforts to map unconsolidated surficial deposits at small (1:500,000), intermediate (1:100,000), and large (1:24,000) scales (Demsey, 1989; Field and Pearthree, 1992; Hunt, 1978; Jackson, 1990). The impetus for surficial geologic mapping lies in the fact that humans have a vested interest in knowing the distribution and nature of late Cenozoic geological deposits and landforms. Most of the Southwest's urban areas including Albuquerque, El Paso, Las Vegas, Phoenix, and Tucson lie on basin fill. Consequently, there is an interest in the physical properties of the substrata, the distribution of industrial minerals, and the potential for flooding and other geologic hazards. These types of information can be obtained from surficial geologic mapping (Pearthree, 1991). In addition to engineering concerns, other research-oriented information can be gained as well. Because surficial geologic mapping is based on temporally discrete geomorphic surfaces, it provides insight into climatic and tectonic mechanisms of landscape evolution (Bull, 1991). Also, surficial geologic maps can be used to assess subsurface archaeological potential (Davidson, 1985) and serve as a guide for avoiding archaeologically sensitive areas.

The Tucson 1o x 2o quadrangle exhibits a wide variety of basin landforms and late Cenozoic surficial geologic deposits. Several factors contribute to this diversity. The Tucson quadrangle spans the transition between the relatively low ranges and typically undissected basins of south-central Arizona and the higher ranges and typically dissected basins of southeastern Arizona. Dissected basins have been dominated by base-level lowering of axial streams and their tributaries, while undissected basins have had relatively stable base-levels. The higher ranges of the eastern half of the quadrangle receive more precipitation due to orographic lifting of moist air. This Is superimposed on a distinct regional climatic gradient, with increasing annual precipitation and cooler annual temperatures from west to cast across the quadrangle. Lithologies vary dramatically both within mountain ranges and between ranges; in some cases, rock type appears to profoundly affect piedmont evolution. Scale 1:250,000

This report provides baseline information on the physical characteristics of the Santa Cruz River to be used by the Arizona Stream Navigability Commission in its determination of the potential navigability of the Santa Cruz River at the time of Statehood. The primary goals of this report are: (1) to give a descriptive overview of the geography, geology, climatology, vegetation and hydrology that define the character of the Santa Cruz River; and, (2) to describe how the character of the Santa Cruz River has changed since the time of Statehood with special focus on the stream flow conditions and geomorphic changes such as channel change and movement. This report is based on a review of the available literature and analyses of historical survey maps, aerial photographs, and U.S. Geological Survey stream gage records.

This report, accompanying maps and GIS data describe the surficial geology, geomorphology, and geologic hazards of the rapidly developing Amado-Tubac area, south of the Green Valley area. The mapping covers the Amado and Tubac 7 1/2’ quadrangles (Figure 1). The map area is in unincorporated Santa Cruz and southern Pima Counties. It includes much of the southern part of the upper Santa Cruz Valley, between the Santa Rita Mountains on the east and the Tumacacori Mountains on the west. There are several potentially conflicting land use issues in the area covered by these maps. The Santa Rita and Tumacacori mountain ranges are public lands owned by the U.S. Forest Service. Several large ranches are located within the mapping area and are interspersed with state trust lands. Urbanization has occurred, and continues to occur, along the Santa Cruz River and around the communities of Arivaca Junction, Tubac, and Rio Rico, just south of the map area. Many areas of the Santa Rita piedmont have been subdivided and prepared for development, although development remains sparse. This report is intended to enhance our understanding of the surficial geology of the Amado-Tubac area and to aid in assessing and understanding geologic hazards in this area. (1 report, 2 map sheets; 1:24,000 scale; UTM Zone 12 projection).

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.

This report and accompanying maps describe the surficial geology, geomorphology, and geologic hazards of the rapidly developing Green Valley – Sahuarita area on the southern fringe of the Tucson metropolitan area. The mapping covers the Esperanza Mill, Green Valley, Sahuarita, and Twin Buttes 7 1/2’ quadrangles (Figure 1). Most of the area is in unincorporated Pima County, but it includes the small but rapidly growing Town of Sahuarita. The whole map area is within the drainage basin of the Santa Cruz River, a major, north-flowing regional drainage that roughly bisects the four quadrangles. These maps cover most of the Santa Cruz Valley (this area can also be considered the southern part of the Tucson basin) between the Santa Rita Mountains on the east to the Sierrita Mountains on the west. There are several potentially conflicting land use issues in the area covered by these maps. It encompasses the southern fringe of the Tucson metropolitan area, which is experiencing rapid development and population growth. The western part of the map area includes several large open-pit copper mines that have been active for several decades. Much of the eastern part of map area is within the Santa Rita Experimental Range and Wildlife Area, a government-owned preserve that is undeveloped and will remain that way for the foreseeable future. Intense urban development has occurred and is continuing in the Green Valley area. Major developments have been proposed for the Canoa Ranch area along the Santa Cruz River. Rapid development is beginning in Sahuarita, which is on the suburban fringe of the Tucson metropolitan area. This report is intended to enhance our understanding of the surficial geology of the Green Valley – Sahuarita area and to aid in assessing and understanding geologic hazards in this area. This new mapping complements previously published mapping that focused on the bedrock in the area (Drewes, 1971; Cooper, 1973). Map focus is Holocene - Pleistocene alluvium and river deposits. Bedrock is undifferentiated. (map scale:1:24,000; projection: UTM Zone 12, NAD83).