The Wellton-Mohawk Irrigation and Drainage District occupies a valley and adjoining mesa along the lower Gila River, in the southwestern part of the State of Arizona. The area has been irrigated for centuries, and now shows problems which reflect past and present water management. First, the water supplies came from the Gila River; later, the groundwater reservoir was used and within about 30 years, groundwater levels declined and salt accumulation, as a consequence of water recirculation, put a limit on attempts to maintain irrigated agriculture. Recently, Colorado River water was brought into the area as the solution to assure permanent large-scale irrigation development. The application of water for crops and leaching of salts caused serious drainage problems. Salinity also caused a problem out of the District as drainage water from the aquifer with high salt content reached the Colorado River and became a source of friction between the United States and Mexico. The water conveyance system in the District is unique in that irrigation water is pumped up the valley into the distribution system. During flood flows along the lower Gila River, this leads to the situation where water is going down the River with little chance to be used, and goes up the valley through a sophisticated conveyance system. Flood flows along the lower Gila River are dependent on infrequent releases from Painted Rock Reservoir, at the upstream boundary of the lower Gila River. The few times they have occurred (2 in 15 years), they created high groundwater levels which were damaging to crop production. The water problems in the District could have short-run solutions through technically possible and economically feasible management practices. The objectives of the study are focused on better use of the water resources, reduction of risks of flood damages, and decrease of salt content of water being diverted to Mexico. A mathematical model was developed to analyze the impact of selected alternatives which could meet these objectives upon the hydrologic system of the District. The application of Strategy I, which proposes the increase of the irrigated acreage by about 5,000 acres, proved to be impracticable under present management conditions since the amount of drainage water to be disposed would be greater than the capacity of the disposal system. Strategies II, III, and IV, which propose increasing levels of change from flood to sprinkler irrigation (25, 50 and 100 rcent) showed results that although not economically encouraging, provide, however, for solution of the internal water problem of the area, and substantial decrease of drainage flow of high salt content delivered to the Colorado River. Strategies V and VI, which proposed reduction by 50 percent or complete elimination of riparian vegetation also proved to be impracticable. Under present management conditions in the District, phreatophytes are an important auxiliary of the water discharge system of the area. Strategies VII and VIII showed that the combination of changes to sprinkler irrigation and reduction of riparian vegetation at levels proposed (50 and 100 percent) practically counteract each other in terms of drainage water to be pumped and does not achieve the proposed objectives. Change in the water management system of the Wellton-Mohawk District would solve its water problems and significantly reduce salinity of the Colorado River water at Morelos Dam, for which hundreds of millions of dollars will be expended in a desalting complex. Drainage from excessive irrigation on the mesa flowing into the valley aquifer is the main cause of high groundwater levels there. Riparian vegetation, although increasing flood damages, is indispensable under the present management system.

The Atlas Mine is located on the northwest flank of the Silver Bell mountains; Silver Bell mining district, Pima County, Arizona. The deposit is high grade (?) sine-copper mineralization in an altered sedimentary sequence. Rocks in the area include Precambrian (?) alaskite; Permian (?) limestone, quartzite and siltstone; Tertiary (?) monzonite, quartz monzonite, quarts latite porphyry and dacite porphyry; and Quaternary alluvium. The limestone has been largely metamorphosed to a mass of tactite, siltstone has been locally metamorphosed to hornfels, and the quartzite has been silicified, locally shattered and altered. Mineralization is related to NE and E-W trending fault systems, and similarly trending intrusive dikes. Predominate ore minerals are sphalerite and chalcopyrite, associated with pyrite, specular hematite and “high temperature" silicates. Copper mineralization is related to the silicified sediments. Zinc mineralization is present in silicates but is more predominate in areas of recrystallized calcite and extensive garnetization, suggesting incomplete replacement of the original sediments by the silicates. Further exploration and development should be undertaken in areas of favorable structural control, and adjacent to favored intrusives.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 218-228). Available also in a digital version from Dissertation Abstracts.

Cognition and social values prevail in urban evolution. Analysis of these values reconstruct an era that has largely vanished; the context is historic downtown Tucson, and the significance is the Mexican enclave that had La Placita as its social focus. The historical evolution and the urban character of La Placita and its surrounding barrio is documented with emphasis on the social meaning of its change. A newly developed cognitive theory of vantages and coordinates provides a model to depict the viewpoints that defined urban development in Tucson. The analysis of personal viewpoint provides a statement of the manner that social values and cognition shaped architecture and urban change throughout the years of growth in the center of Tucson.

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