Originally posted by Bob Harris this was once an ancient seabed from what I understand, millions of years of stacked sediment. GeoJerry could explain this better than I.
Bob, the colors in sandstones are generally a function of the type of iron oxides present in the original sediments. You can have different oxides like magnetite (Fe3O4), hematite (Fe2O3), or goethite (FeOOH) among many, and these different oxides tend to generate their own brand of color, so depending on the oxide concentrations (can be mixtures), temperatures, etc, you get different colors. Generally speaking, warm colors, like the reddish sandstones, indicate non-marine environments, like alluvial or river deposits where iron oxides form a rust red color. The darker colors (especially grays and greens) tend to be of marine origin, deposited below sea level under different oxidizing conditions. The original layer geometry is often obscured in canyons like this, where rock debris erodes off higher surfaces and coats the walls of the canyons.