The Petrified Forest National Park This high dry tableland was once a vast floodplain crossed by many streams. To the south pine like trees grew along the headland and crocodile reptiles and dinosaurs lived among a variety of ferns. The trees were washed by swollen streams into silt and mud and volcanic ash then covered logs gradually silica bearing groundwaters seeped through the logs and bit by bit replaced the original wood tissues with silica deposits