The Permian in Colorado, US

Paleontology and geology

Erosion of the Ancestral Rockies near Denver in a semi-arid climate produced abundant sand and led to the deposition of extensive dunes. These sand dune deposits are mined today for flagstones. Tracks of insects and unknown reptiles that lived on the dunes can be found on these flagstones. Manganese dendrites on the flagstones are commonly mistaken for fossil ferns.