Petrified Forest, Petrified forest in Sonoma County, United States.

Petrified Forest is a hillside site in Sonoma County where grey and black petrified logs lie on a grassy slope, broken into thick rectangular segments with grooved surfaces and pale weathering along the edges. The largest piece, nicknamed "The Giant", is 60 feet long and 6 feet wide, and a brown sign with yellow lettering marks it. Other named logs include "The Queen", 65 feet long and 8 feet wide.

A volcanic eruption at Mount St. Helena about 3.4 million years ago buried the trees, and petrification took thousands of years. In 1870 Othniel Charles Marsh identified the trees as Sequoia langsdorfii; Robert Louis Stevenson later described the site in The Silverado Squatters (1883). Ollie Orre Bockee bought the land around 1912 for $14,000, opened it to tourists around 1914, and her descendants still run it. It was listed as a California Historical Landmark on January 31, 1978.

The site's name comes from the stone-like trees that dominate the landscape like natural monuments. Visitors today can observe how nature transformed living wood into rock and sense the power behind this transformation.

The forest lies near Calistoga in Sonoma County and is reached by a walking route past the fallen logs, where a brown sign gives the measurements of "The Giant": 60 feet long and 6 feet wide. Ground beside the logs is uneven and grassy, so wear sturdy shoes. The property reopened after damage from the 2017 Napa and Sonoma fires.

Redwood trees were gradually transformed into stone by volcanic ash and minerals about 3.4 million years ago. This transformation is so complete that the petrified trees today look like natural sculptures created by the power of the earth.