The Old Faithful Geyser of California, located off Tubbs Lane in between Route 128 and Route 29 in Calistoga, is one of three geysers in the world with the designation "old faithful." Like its more famous Yellowstone counterpart, the Napa Valley geyser erupts at regular intervals--approximately every thirty minutes, but heavily dependent on environmental externalities like temperate and rainfall--spraying steam and scalding water 60 to 100-feet in the air.
The water for the Old Faithful Geyser of California comes from an underground river. When this water flows over the hot molten magma deep in the earth, it boils and expands and is collected in large cavities. Under tremendous pressure from the heat, and assisted by a constriction of the passage upward, the superheated water is forced through the fissures and fractures and erupts with an outpouring of steam followed by a fulmination of hot dancing water.
Under normal conditions, the water, the heat and the underground structure all remain constant and for this reason Old Faithful erupts regularly. However, the geyser has also proven itself to be a good predictor of earthquakes. When the geyser's show is delayed or diminished, an earthquake is likely within the next couple of weeks in the 500 miles surrounding the geyser.