In the Salton Trough, of southern California and northern Baja California, the most important geothermal fields are those at the Salton Sea (SSGF) and Cerro Prieto (CPGF). They have nearly the same geologic framework; both are located in active pull-apart basins within the Trough, an actively growing rift valley which is the northern landward extension of the Gulf of California. The lithologic columns in these fields are dominated by deltaic and alluvial deposits, with that of the SSGF being richer in lacustrine sediments and evaporites. The heat sources in both fields are oceanic ridge-type intrusions of sheeted dike complexes. The volcanoes found in the CP and SS areas are genetically related to the hypabyssal rocks intercepted by some of the geothermal wells. The maximum temperatures measured in the wells are similar (i.e., around 350-370? C).

The main difference between the two fields is in the salinity of the geothermal fluids. The maximum total dissolved solids in the SSGF geothermal brines is about 30% and only about 3% in CPGF brines. The hydrogeological regimes and the lithology prevailing in these fields could reflect this contrast.

In spite of their similarities, the difference in the rate of field development has been enormous. Although the SSGF was discovered earlier and seems to have a larger energy potential, the CPGF was developed faster, at present having more than twice the capacity installed at SSGF. This was largely due to the high salinity (and corrosivity) of the SSGF brines. It took intensive research to develop the technology to handle these brines at the surface, separate the steam for electrical generation, and inject the waste brine safely. Other important factors influencing field development were the dissimilar economic and regulatory conditions in Mexico and the US.

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