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)

This report summarizes the surficial geology and geomorphology around the western part of the Crater Range, situated in the North Tactical Range on the Barry M. Goldwater Air Force Range in southwestern Arizona (Figure 1). The purpose of these investigations is to describe the geologic and geomorphic framework of the western Crater Range and surrounding areas in conjunction with an archaeological survey that was conducted for the Air Force by SWCA, Inc, and Arcadis Geraghty and Miller (Tucker, 2000). Field investigations and mapping were done in the spring of 1998. A 1:24,000-scale map showing the surficial geology of the survey area is included with this report (Plate 1). Interpretation of aerial photographs, field checking, and mapping was done primarily by J. Klawon, with field assistance and suggestions from P. Pearthree. Several previous geologic investigations have been conducted in this area. Kirk Bryan explored this area as part of a project to locate and evaluate potential water sources (Bryan, 1925). He described the general geology and physiography of this area, and made many astute observations about the processes that have shaped this landscape. This portion of Arizona was mapped on a reconnaissance basis by E.D. Wilson and R.T. Moore as part of their efforts to develop a 1:500,000-scale geologic map of Arizona (Wilson and others, 1969). The bedrock geology of the Ajo 1:250,000-scale sheet, which includes the project area, was subsequently mapped in somewhat more detail by Gray and others (1988). The generalized surficial geology of the Ajo sheet was mapped by Morrison (1983) at 1:250,000 scale. Bull (1991) developed a conceptual framework for understanding the impacts of climatic changes on arid region fluvial systems of the lower Colorado River region.

This report summarizes the surficial geology and geomorphology of the Tinajas Altas area on the Barry M. Goldwater Air Force Range in southwestern Arizona (Figure 1). The purpose of these investigations is to provide a geologic and geomorphic framework for an archaeological survey of this area. The geologic map included with this report covers parts of several 1:24,000-scale topographic quadrangles that cover the study area (Plate 1). Interpretation of aerial photographs was done primarily by Karen Demsey, with review and field checking by Thomas Biggs, with field assistance from Philip Pearthree of the Arizona Geological Survey. Map compilation and report preparation was done by Biggs; final editing and formatting of this report was done by Pearthree.

Throughout the southwestern United States, vegetation in what historically was grassland has changed to a mixture of trees and shrubs; exotic grass species and undesirable shrubs have also invaded the grasslands at the expense of native grasses. The availability and amount of soil nutrients influence the relative success of plants, but few studies have examined fire effects on soil characteristics in a temporal, spatial, and species group specific fashion. Likewise, few studies have tied fire effects and ecological aspects to the underlying geology. Our research investigates the effects of fire events on selected soil characteristics pH, nitrate (NO3-), plant-available phosphorus (PO4 -3), and total organic carbon (TOC) on native grass-, exotic grass-, and mixed grass-dominated plots distributed on four different geological surfaces. Treated and control plots were sampled prior to burn treatment and at intervals after the burns. In addition to new geologic mapping of the study areas, results indicate the geologic substrate is the most important variable for explaining pH, NO3- and PO4-3 values in the soils. Dominant grass type –native, non-native, or mixed – had little effect on the response of soil geochemistry to fire events: post-burn results indicate vegetation was a significant factor only for TOC. Recovery to pre-burn levels varies with characteristic: there were no significant initial differences between vegetation types, but significant differences in NO3-, PO4-3, and TOC amounts occur as a result of fire events, geological characteristics, and time. The research helps identify the soil response to fire and the recovery times of soil characteristics, further defines which fire frequency is optimal as a management strategy to maximize soil macronutrient contents, and illustrates the important role geology plays in grassland ecosystems.