A Slice Through Time
September 19, 2001
The striking contrast between the light buff colored Coconino Sandstone and the muddy red Hermit Shale is cause for this portrait of rock wall along the Bright Angel trail in the Grand Canyon. The easily eroded shale was deposited as mud in flood plains and tidal flats, and owes its red color to iron oxides. Fossilized reptile tracks and plants are found in the shale. The mud flats dried and cracked as they were overrun by advancing sand dunes. The tilted bedding and uniform size and purity of the quartz grains of the Coconino formation indicates deposition as wind-blown sand. Some of that sand can be seen filling a deep crack in the underlying red shale (right center).