"Petrified wood with dry desert grass and soil in foreground. The colors of ochre and red in this specimen excavated from Petrified Forest National Park in Arizona are result of iron minerals that soaked into the plant cells during Late Triassic Epoch converting them to stone. White traces are silica. This sample and the petrification in the area is part of the Chinle geological formation from that period. Although the park is characterized primarily by arid grassland today, some 200 million years ago it was a fluvial plain with river habitat, forests and dinosaurs."