Petrified Forest National Park is a United States national park in Navajo and Apache counties in northeastern Arizona. The park's headquarters are about 26 miles (42 km) east of Holbrook along Interstate 40 (I-40), which parallels a railroad line, the Puerco River, and historic U.S. Route 66, all crossing the park roughly east–west. Named for its large deposits of petrified wood, the park covers about 146 square miles (380 km2), encompassing semi-desert shrub steppe as well as highly eroded and colorful badlands. The site, the northern part of which extends into the Painted Desert, was declared a National Monument in 1906 and a national park in 1962. About 600,000 people visit the park each year and take part in activities including sightseeing, photography, hiking, and backpacking.