Tectonic geomorphology of the Toroweap Fault, western Grand Canyon, Arizona: implications for transgression of faulting on the Colorado Plateau. The Toroweap fault is a major normal fault in Northwestern Arizona. Along its southern end are four displaced Quaternary surfaces, three of which have measurable displacements that are multiples of about 2.2 m. Soil carbonate analysis was carried out to estimate ages for the three surfaces. An extrapolated carbonate accumulation was used to estimate an age for the oldest surface of between 26 and 54 ka; the youngest displaced surface is between 4 and 11 ka. Oldest undisplaced surface is 2 ± 1 ka. Diffusion modelling determined the most recent surface rupture to be 3 ± 1 ka. An aid in determining degree of tectonic activity where displaced materials are not present is the escarpment sinuosity index (Es). Escarpment length was divided by fault length. Because cliff height varies from one area to another, the index was normalized by dividing by total cliff height. The index is inversely proportional to total displacement. Segments of the fault were distinguished using Es, presence and style of Quaternary displacements, and changes in fault orientation. There are five segments in the study area, the most active segment spanning the Grand Canyon. Report and two map sheets, map scale 1:24,000.

Radon gas, which is produced by the radioactive decay of uranium, can accumulate in homes to levels that are considered hazardous by the U.S. Environmental Protection Agency. Hazardous indoor-radon levels are most common in areas where underlying rock and soil contain unusually high levels of uranium. Anomalous uranium levels are present at scattered locations in Arizona. Many of these localities are associated with uranium mines but others are not and may be inconspicuous. Homes or buildings that are built on such areas are at risk for having hazardous levels of indoor radon gas. This bibliography is intended to help the user in locating studies of uranium and radon in Arizona that could be useful in estimating the probability of high uranium levels in geologic materials. This knowledge may help home builders and others in avoiding radon gas and may assist scientists and those engaged in uranium exploration. ( 50 pages)

Map showing names and outlines of physiographic areas in Arizona used by the Arizona Geological Survey with base map showing township and range. Map scale 1:1,000,000

Previous workers have established the general petrological character of the McCoy Mountains Formation and equivalent Jurassic-Cretaceous units in southwestern Arizona and southeastern California by point-counting the detrital modes of 170 sandstones and metasandstones (Robison, 1979; Harding, 1980, 1982; Harding and Coney, 1985; Laubach et aI., 1987; Richard et aI., 1987; Fackler-Adams et aI., 1997). Many of the samples studied, however, are foliated to varying degrees, with neomorphic growth of metamorphic minerals partly obscuring detrital textures and compositions. For this report, a set of control samples was collected from the least deformed and least altered rocks that could be found exposed in mountain ranges of southwestern Arizona.

Beginning in the mid-1860s the southwestern US experienced a mining boom, and a large number of mines were developed. They went through alternating phases of economic upswing and decline, but by the end of the 1940s most of the smaller mines had been abandoned for good (Woznicki 1987, Beck and Haase 1989). Nevertheless, their tailing, waste rock dumps and acid mine drainage still represent an environmental hazard because of the heavy metals released from them (Young and Clark 1978, Marcus 1987, Rampe and Runnels 1989, Rosner 1995a, 1996, 1998, Graf et al. 1991, Hyde 1994, Lind and Hem 1993). The metals can either be leached directly into the groundwater and the surface water (Young and Clark 1978, Lind and Hem 1993) or accumulate in soils and sediments (Brummer et al. 1986, Bradley 1989, Moore and Luoma 1990, Schachtschabel et al. 1992). Under certain circumstances they can be redissolved and become available to plants or enter the groundwater with the percolation water (Young and Clark 1978, Bergmann 1989, Herms 1989, Sauerbeck 1989). This article will deal only with heavy metals in fluvial sediments and in soils; the contamination of water and vegetation in the study area (cf. below) was dealt with in recent publications (Rosner 1995b, 1996, 1998).

Groundwater and surface water quality was analyzed in several watersheds of the historic mining district of Chloride and the southern adjacent former mining areas on the western slope of the Cerbat Mountains, northwest of Kingman, in Mohave County, Arizona. The investigations were carried out to characterize the general water quality, and particularly to ascertain, to what degree groundwater and surface water are contaminated due to the past mining activities. Groundwater in the immediate vicinity of the large Tennessee Mine, where ore processing took place, was found to be seriously polluted by heavy metals. But neither the groundwater in the town of Chloride, nor the groundwater in the Cerbat Wash watershed, showed evidence of contamination by subsurface or surface water flow from the upstream mining areas. Independent of the historic mining nitrogen contamination was found in the Chloride wells, which could be attributed to improperly functioning private septic tanks. In contrast to the groundwater almost all surface waters were contaminated by heavy metals and other contaminants due to the historic mining activities.

Geologic Map of the Salome 30' x 60' Quadrangle, West-central Arizona. One map sheet and one report (33 pages).

Land subsidence and related earth fissures have become widespread occurrences in southern Arizona. As the areal and vertical extent of subsidence has increased, more earth fissures have been discovered. As a result, there is growing concern about existing and potential damage caused by these phenomena. This concern is reflected by the increasing number of requests for information received by the Arizona Geological Survey (AZGS), which has prompted the compilation of this bibliography, establishment of a Steering Committee on Subsidence and Earth Fissures, and formation of the Center for Land-Subsidence and Earth-Fissure Information (CLASEFI), which is supported jointly by the AZGS and the Arizona Department of Water Resources. Although many human-induced and natural processes give rise to land subsidence and earth fissures, those in southern Arizona are closely linked to long-term extraction of ground water by man. This bibliography, therefore, focuses on subsidence resulting from ground-water withdrawal. As ground water is removed from some alluvial aquifers, sediment particles in those aquifers lose some of their ability to support the overburden, the grains become more closely packed, and aquifer volume decreases. The land surface sinks (subsides) in response to the decreased aquifer volume at depth. This type of subsidence proceeds gradually, but, with time, can spread over large areas and cause significant deformation. ( 21 pages)

This report is a compilation of available data on Quaternary faults in Arizona as of the summer of 1998. These data were compiled as part of a effort to compile data and map information on Quaternary faults throughout the world, which is being overseen by Michael Machette of the U.S. Geological Survey. Michael Machette, Richard Dart, and Kathleen Haller provided substantial technical assistance in the preparation of these data, and the fault data forms were reviewed and edited by Michael Machette. As part of this effort, fault traces were entered into a Geographic Information System (GIS) database by the USGS. Map traces were plotted on 1:250,000-scale topographic base maps, and were digitized by Richard Dart and Lee-Ann Bradley of the USGS. They generated the 1:750,000-scale fault map that accompanies this database. neotectonic structures in Arizona. The first and most comprehensive of these is the state-wide compilation of neotectonic faults by Menges and Pearthree (1983), which was done primarily by Chris Menges. I also utilized the later state-wide compilation of young faults by Euge and others (1992). Regional compilations of the Douglas and Silver City 1:250,000-scale quadrangles in southeastern Arizona by Machette and others (1986) and the Flagstaff area by Pearthree and others (1996) provided most of the data for these areas. I also utilized indexes of geologic mapping in Arizona (Scarborough and Coney, 1982; Harris and others, 1994) and the geologic bibliography for the state (Trapp, 1996) developed by the Arizona Geological Survey. The data structure is set up to provide systematic information on each fault zone. Each fault has been assigned a number as part of the world-wide fault data set; faults are identified by number on the accompanying map. Fault names are based on published maps or reports. In cases where different names have been used for the fault, the alternative names are listed within the database. All of the faults are listed by name and number in the table on the following page. This table indicates where the data summary for each fault can be found, as well as the age of youngest activity and fault slip rate category. The individual fault data sheets include information on map and data sources, fault location, geologic setting of the fault, the geomorphic expression of the fault, recency of fault movement, fault slip rate(s), and fault zone length and orientation. Fault locations are rated good if they were originally mapped at 1:62,500 scale or larger, moderate if they were mapped at 1:130,000 scale or larger, or poor if there is substantial uncertainty in their location because of weak surface expression. Faults were grouped into slip rate categories of <0.02 mm/yr, < 0.2 mm/yr, and <1 mm/yr. Reported lengths are for the whole fault zone, not cumulative length of each individual fault in the zone, and orientations are averages for the fault zone. A composite list of references is at the end of this report. These fault data can be readily updated. Any feedback or any further data regarding individual faults is welcome, and more faults can be added as they are identified. (122 pages)

We have completed initial paleoseismologic investigations to evaluate the recency and size of paleoearthquakes and long-term slip rates on the Hurricane fault in southern Utah and northern Arizona (SUNA). The Hurricane fault is a long, west-dipping normal fault with substantial late Cenozoic displacement within the structural and seismic transition between the Colorado Plateau and the Basin and Range province. Previous reconnaissance studies of the fault in northern Arizona and southern Utah had documented evidence of late Quaternary activity. Because of its great length, the Hurricane fault almost certainly ruptures in segments, and abundant geometric and structural characteristics suggestive of fault segmentation exist along its trace. Our efforts have focused on a systematic, detailed reconnaissance of the fault from the Utah-Arizona border north to Cedar City and a detailed investigation of 20 km of the fault from the border southward into Arizona. In addition, we conducted detailed reconnaissance investigations of the fault in Whitmore Canyon north of the Colorado River. ( 137 pages)