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About as fast as toenails grow, the Imperial Valley continues to widen in an east-west direction. As fast as fingernails grow, Imperial Valley's west side shudders northwestward relative to territory farther east and north. The combined extensional and sideways drift taking place across Imperial County occurs mostly in the southernmost San Andreas Fault Zone, which lies buried beneath the Salton Sea and the fertile fields of the Imperial Valley. The ripping apart of the tectonic plates there has produced geologic fireworks in the past, as well as some less dramatic surface activity taking place even now.

For a look at two of Imperial Valley's best geologic sites, steer your car east on Interstate 8 toward El Centro. Just short of El Centro, exit at Forrester Road and drive about 20 minutes north to the tiny farming community of Westmorland. Continue north, crossing Highway 78, staying on Forrester. After two forced sharp turns, you will be northbound on Gentry Road.

On the horizon ahead, you'll spot at least one of the valley's four large geothermal electric power plants, which are for good reason these days puffing at full capacity. Make a left at Lindsay Road, shy of the first power plant, and drive to Lack Road. A right turn at Lack puts you atop a levee, with the waters of the Salton Sea on the left. The sea's water level has been on the rise in recent years. After a couple of turns ahead, park alongside two low hills on the right. The larger one is called Obsidian Butte and is composed primarily of obsidian, or black volcanic glass. Obsidian is produced when magma cools very suddenly so that there is no time for mineral crystals to form. The resulting rock has a structure similar to glass. In ancient and modern times obsidian has been honed into ultra-sharp arrowheads, knives, and cutting tools, so be careful when handling the stuff.

After visiting Obsidian Butte, go back to Lindsay Road and work your way indirectly over to English Road, where you turn north. Cross Sinclair Road and turn left on the third road ahead — a dirt road signed "Schrimpf Road," which is actually the middle of three closely spaced roads initially heading west. Just after the main Schrimpf Road turns north and becomes Davis Road, park and walk over a short distance to the volcanic "mud pots" out in the middle of an empty field. Here, and in a few other spots within a few miles, carbon dioxide rises to the surface and pushes up water from a shallow aquifer. Sulfurous odors waft on the breeze, and hisses, burps, and other rude noises emanate from shallow pools and conical mounds of mud being built in front of your very eyes. A couple of weeks ago the temperature of the mud ranged from warm to almost scalding -- as reported by my 12-year-old son, who felt compelled to explore the intimate recesses of nearly every active vent with his right hand and arm.

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