In US about 2700MW of power is generated from geothermal energy, but let me inform you that this is less than half percent of the total power generated in US. At present electricity from geothermal energy is being produced in only four states, these are: California, Nevada, Hawaii and Utah.
In California there are about 14 areas where geothermal energy can be used to produce electricity. In some places the energy is less or the water is not hot enough to be used for producing electricity. The main spots of geothermal energy reservoir are:
1) Some areas in north of San Francisco
2) Areas around Volcanic National Park
3) Places around Mammoth Lakes.
4) Areas surrounding Coso Hot Springs.
5) The region of Imperial Valley in south California.