Petrified Forest National Park

Eastern Arizona

This national park is an extraordinary sight: the Painted Desert here is strewn with fossilized logs predating the dinosaurs. The 'trees' are fragmented, fossilized 225-million-year-old logs scattered over a vast area of semidesert grassland. Many are huge – up to 6ft in diameter – and at least one spans a ravine to form a natural bridge. A 28-mile road meanders through the park, between I-40 and Hwy 180 to the south. The highest concentration of trees is by the south entrance.

The trees arrived via major floods, only to be buried beneath silica-rich volcanic ash before they could decompose. Groundwater dissolved the silica, carried it through the logs and crystallized it into solid, sparkly quartz mashed up with iron, carbon, manganese and other minerals. Uplift and erosion eventually exposed the logs.