Old Faithful Geyser of Calistoga, California, is neither faithful nor a geyser, but it's pretty close. A local settler tapped the geothermal reservoir here in 1870, and the hole he drilled began the spontaneous cycle of eruption and quiescence that marks a true geyser.

The eruptions come anywhere from 10 to 50 minutes apart, but at any one time they're fairly regular. Detailed logs of the eruption times were kept for many years by the owner. When geologists came looking for evidence of earthquake precursors, these records looked very interesting: some significant quakes occurred shortly after changes in the timing of Old Faithful. It seemed that the underground system was highly sensitive to the regional state of crustal stress. But the eruptions also varied for other reasons, including no reason at all, and the hypothesis was abandoned.