Geothermal power could account for 10% of U.S. energy production

The study concludes that geothermal is proven, could impose markedly lower environmental impacts than fossil-fuel and nuclear power plants, and is likely to be cost-competitive with the alternatives. This coverage in LiveScience points out how big a player geothermal already is in the US:

"The United States is the world's biggest producer of geothermal energy. Nafi Toksöz, a geophysicist at MIT, noted that the electricity produced annually by geothermal plants now in use in California, Hawaii, Utah, and Nevada is comparable to that produced by solar and wind power combined."