This 23 page report is an initial investigation into the role that low-angle faulting may play in the formation of the Thermo Hot Springs Known Geothermal Area (KGRA), within the Sevier geothermal anomaly of southwestern Utah. The stratigraphy and structures exposed in the southern mineral mountains are used as an analog for studying the subsurface stratigraphy and the detachment fault within the Thermo Hot Springs KGRA.

Since the Arab oil embargo of 1974, it has been clear that the days of almost limitless quantities of low-cost energy have passed. In addition, ever worsening pollution due to fossil fuel consumption, for instance oil and chemical spills, strip mining, sulphur emission and accumulation of solid wastes, has, among other things, led to an increase of as much as 10% in the carbon dioxide content of the atmosphere in this century. This has induced a warming trend through the 'greenhouse effect' which prevents infrared radiation from leaving it. Many people think the average planetary temperatures may rise by 4°C or so by 2050. This is probably true since Antarctic ice cores evidence indicates that, over the last 160000 years, ice ages coincided with reduced levels of carbon dioxide and warmer interglacial episodes with increased levels of the gas in the atmosphere. Consequently, such an elevation of temperature over such a relatively short span of time would have catastrophic results in terms of rising sea level and associated flooding of vast tracts of low-lying lands. Reducing the burning of fossil fuels makes sense on both economic and environmental grounds. One of the most attractive alternatives is geothermal resources, especially in developing countries, for instance in El Salvador where geothermal energy provides about a fifth of total installed electrical power already. In fact, by the middle 1980s, at least 121 geothermal power plants were operating worldwide, most being of the dry steam type.

Past exploration in low- and moderate-temperature systems of the Great Basin shows that the relatively small area associated with fluid upflow and elevated temperatures is often difficult to detect by drilling widely spaced temperature-gradient holes or by other methods. By studying the Newcastle geothermal system, we hoped to develop a basic understanding of the concealed hydrothemlal system as a tool for assessing other geothermal areas of the Great Basin. The emphasis of our work centered on determining (1) the distribution of subsurface heat and the movement of thermal fluid, (2) the location and geometry of bedrock structures that might control fluid movements, (3) the chemical character of the geothermal water, and (4) the geometry of the bedrock beneath the Escalante Desert. Field studies included: (1) drilling and monitoring temperatures in shallow themlal-gradient boreholes, (2) mapping geologic units and performing structural studies in the adjacent mountains, (3) conducting detailed gravity surveys, (4) conducting electrical resistivity and self-potential (SP) surveys, (5) collecting water samples for detennining major ions and light stable isotope analyses, and (6) mapping Quaternary units.