A few hours east of San Diego is the Salton Sea, an inland lake formed by periodic overflows of the Colorado River. By chance, this low-lying region (the lake is currently 69 m/226 ft below sea level) is also above some shallow magma. Five necks of a rhyolitic volcano from 16,000 years ago are underneath. Consequently, geothermal energy is abundant.
Hot springs are found throughout the area (some the size of football fields), but the most fun to visit are popularly called the Mud Volcanos. Rising carbon dioxide gas pushes up hot water from below, but not with Yellowstone geyser pressure, more like a soft bubbling flow. Fine gray mud pools at the surface, and builds up into soft beehive-like structures.
My wife and I used an infrared thermometer to measure the surface temperature of the mud, and the hottest we found was around 150°F/66°C. The main gas at this particular site is carbon dioxide, which is odorless, and so there’s no rotten egg smell like that found at many other geothermal sites.
Geothermal plants are popping up quickly all around, in fact there is now one adjacent to the mud volcanos so new that it doesn’t even show up on Google Earth imagery as of this writing. One plan to revitalize the polluted and oversalinated Salton Sea involves using this “free” electricity to pump water from the Sea of Cortez to the south, desalinate it, send the brine to a wetlands in Mexico that needs it, and sell the excess fresh water.
If you’d like to visit the mud volcanos yourself, here’s a link to a Google Map that will take you right to them. Enjoy!