The Permian in the Grand Canyon consists of four layers. From the top down, Kaibab Limestone, Toroweap, Coconino Sandstone, and Hermit Shale.
The Kaibab formation was a shallow inland sea at the end of the Permian, dating from 270 million years ago. The Toroweap just below is a mixture of sandstone and limestone formed when the sea was moving into the sand dunes which formed the Coconino.
The Red Hermit Shale was a swamp 230 million years ago. We find fossils of ferns, dragonfly wings, and amphibian tracks. About 250 million years ago, a sand dune sea 70 miles wide swept in to form the Coconino Sandstone. In this layer we only find footprints of reptiles: no reptile fossils.