“At length, in a lonely dell, we came on a huge wooden gate with a sign upon it like an inn. "The Petrified Forest. Proprietor: C. Evans," ran the legend. Within, on a knoll of sward, was the house of the proprietor, and another smaller house hard by to serve as a museum, where photographs and petrifactions were retailed. It was a pure little isle of touristry among these solitary hills.”
–Robert Louis Stevenson, The Silverado Squatters (1883)
Over a hundred years after Stevenson visited the Petrified Forest in Calistoga, California, much remains the same: the hills—now the northern edge of the Napa Valley wine country—are more traveled, but the forest’s ancient pedigree, quiet setting, and touristy touches can still inspire. As one of California’s many wondrous natural museums, the forest lacks the grandeur of the state’s redwood cathedrals, but beats them in history.
For millions of years, what lay beneath the soil here was a mystery. It took until 1857 for a local man to reveal the secret: trees that had turned to stone.
How could this happen? Did Medusa stroll among these woods? Indeed, an otherworldly explanation feels possible, even today, as you explore this prehistoric forest. But the answer is not myth or legend; it is rooted deeply in science. About 3 million years ago, during the Pliocene period, the forest was covered by volcanic ash following the eruption of Mount Saint Helena (not to be confused with Washington state’s Mount Saint Helens) seven miles away. Instead of rotting away like all other organic matter, the trees were sealed pristinely in a tomb of ash. Over time, a mixture of water and silica from the ash seeped into the porous wood, then crystallized into quartz that replaced the original cell structure. For many of these petrified trees, the wood’s architecture remains etched in stone.
Around the world, there are many other forests that were petrified by erupting volcanoes. Some, like those at the Petrified Forest National Park in Arizona, formed when floodwaters buried trees under a thick layer of sediment containing volcanic ash. The result is the same: trees transformed into stony columns nearly as hard as diamonds. The coloring of petrified wood, which can reach rainbow proportions, comes from impurities in the quartz. Minerals such as iron, copper, and manganese will yield a red or yellow hue, a green-blue tint, and a rosy blush. Paleontologists study these jewel-like specimens, ancient people used them as tools, and entrepreneurs have made them a tourist site.