Lichen grows in the geometric crevices of a petrified redwood tree in Yellowstone National Park.
The petrified redwoods are estimated to have been entombed in mud and rock about 50 million years ago.
A petrified tree is protected from souvenir collectors by an iron fence on a Yellowstone National Park hillside. The tree is one of many inside the park, believed to have been preserved after being buried in mud, rock and sand after a volcanic eruption.
This photo from a 1921 survey of the petrified trees shows some of the large preserved trunks on Specimen Ridge in Yellowstone.
A boardwalk leads to a petrified tree in Yellowstone National Park. The petrified tree is the easiest to reach in the park, just off the road between Mammoth Hot Springs and Tower Junction.
A petrified tree makes the perfect perch for a male mountain bluebird.
This photo taken in 1907 shows a second petrified tree stump in the background. The stump is no longer there, having been chipped away by souvenir hunters.