The United States is facing serious energy crisis. It is estimated that the electrical requirements of the United States will reach 5.8 × 10¹² Kwh by 1990. Most of the future electrical power will be produced by conventional generating plants; however a large share will have to be produced by other sources, such as nuclear and geothermal generating plants.

Geothermal resources--the natural heat of the earth's interior--have been used increasingly since the start of the century to generate electricity. The present worldwide geothermal generating capacity has reached nearly 900,000 kw and will probably increase tenfold in the near future.

On a worldwide basis, geothermal exploration efforts today are directed primarily to areas of surface heat leakage in regions which have experienced volcanism in the recent geologic past. Exploration for a commercial geothermal reservoir is similar to that for metalliferous mineral and hydrocarbon deposits, and involves common geologic, geophysical, and geochemical techniques. All conventional geologic exploration methods are used, such as surface and subsurface mapping, and photogeologic and remote sensing techniques to delineate the more favorable parts of the area. In conjunction with geologic mapping, geophysical methods are used. These include surface and shallow-subsurface temperature and heat-flow measurements, heat discharge from springs, rock thermal conductivity measurements and electrical resistivity measurements. The geochemical character of the thermal springs in the region affords a rapid, preliminary evaluation of the reservoir temperature. Among some of the more useful geochemical thermometers used are the chloride and silica contents of the waters and sodium/potassium ratio.

The geothermal resources of Colorado are indicated by 113 thermal springs and wells having a temperature higher than 21°C. Most of these springs and wells are in the southern Rocky Mountains of southwestern Colorado.

The temperature of the thermal waters in Colorado ranges from a low of 21°C at Eldorado Springs to a high of 84°C at

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Hortense Hot Springs. The waters issue from rocks of various compositions, ranging in age from Precambrian to Tertiary.

Sixteen surface or near-surface measurements of flow of heat from the interior of the earth have been made in Colorado and published. These measurements range from a low of 1.4 H.F.U. (heat flow units) at Yellow Creek in the northwest part of the state to a high of 3.7 H.F.U. at Ouray, Colorado, in the San Juan Mountains.

It appears, from interpreting published data, that the San Juan volcanic region of southwestern Colorado has the most potential for the development of a commercial geothermal reservoir.

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