The hook
Giant redwoods turned entirely to stone by a volcanic eruption three million years ago, lying where they fell, near Calistoga.
01Why it's worth it
When Mount St. Helena erupted around 3.4 million years ago, it flattened a redwood grove and buried it in ash, and over time the wood mineralized into solid stone, keeping the grain, the bark, even the rings, while turning to rock. This little roadside forest west of Calistoga is the result: massive petrified logs you can walk up to on a short flat loop, some of the largest petrified trees anywhere. Robert Louis Stevenson wandered through and wrote about it in the 1880s. Set expectations, it's a small, family-run, gently old-fashioned paid attraction, not a national park, so it's a half-hour curiosity rather than a day. But standing next to a redwood that's become granite-hard rock is a strange thing, and it pairs naturally with the volcanic oddities around Calistoga.
02How to experience it
It's on the Petrified Forest Road between Calistoga and Santa Rosa, a small admission and a flat interpretive loop, half an hour or so. It's a fine stop on the way to or from the Sonoma coast; pair it with Old Faithful Geyser nearby for a double dose of Calistoga's volcanic weirdness.