The petrified trees of Napa Valley’s  Petrified Forest (4100 Petrified Forest Rd., Calistoga, 707/942-6667, www.petrifiedforest.org , daily 9 a.m.–5 p.m., summer until 7 p.m., adults $6, seniors/juniors $5, children $3) no longer stand—technically this is an archaeological dig that uncovered a forest that existed more than three million years ago. A volcano that no longer exists erupted, blowing over the trees and covering them with ash.
Over hundreds of thousands of years, the minerals in that ash traded places with the contents of the cells that made up the wood of the trees, “petrifying” them. Now these long-dead trees are made of stone. When you visit the forest, you’ll see plenty of live, upright trees.
Follow your trail map along a 0.5-mile loop to visit the various excavated petrified trees and chunks of trees. You can touch some of the chunks of petrified wood, but most of the large fallen stone trees enjoy the protection of fences to preserve their pristine state.
You’ll get to see one rare petrified pine tree, and a number of petrified Coast Redwoods, almost all of which have names. A fun note: All the trees fell in the same direction (and still face that way), showing us which way the blast came when the volcano blew up.
Inside the visitors center and gift shop, you’ll find lots of rocks and minerals, books on geology, plus a few rare shards of the petrified trees from this very forest.