There's a fire down below Calistoga that's been attracting humans for centuries.
At the northern end of the Napa Valley, a mile or two underground - maybe deeper – water condenses and drips its way into a vast underground reservoir in a layer of fractured rock. Below that, perhaps another mile or more, molten magma swirls and bubbles, heating the water above until it begins to turn to steam. As the steam rises, it heats more water along the way and together the mixture races upward, looking for release.
At its most noticeable exit areas, such as the geyser just north of Calistoga, the heated concoction shoots above ground like a giant sub-service water pistol. The mixture of liquid and steam can reach 350 degrees Fahrenheit and catapult itself 40 feet or more into the air. The geyser is indeed a sight to behold but it isn't the only show in town. For centuries, humans have made pilgrimages to natural hot springs and mud baths in the area, seeking the curative properties of heated water, minerals and mud.
Much of the mud in the area is infused with volcanic ash, said to be particularly effective in pulling toxins from the body. The Wappo Indians, living in the northern valley 8,000 years ago, bathed in the warm sulfur waters and may have used mud for its restorative values as well. The first Europeans in the area - the Spanish - did the same more than 300 years ago and called the area "Agua Caliente."
Resorts began promoting mineral and mud baths in Calistoga more than a century and a half ago. Now more than two dozen spas and hot springs-centered resorts dot the landscape around Calistoga.