Supai Group

The Supai Group is a slope-forming sequence of mixed red beds and limestone outcropping across the Colorado Plateau, including the Grand Canyon in northwest Arizona, southwest Utah's Virgin River valley, and parts of Nevada and California, with exposures also visible at Sedona's Oak Creek Canyon. It dates from the late Bashkirian to Sakmarian stages, roughly 320 to 290 million years ago, spanning the Pennsylvanian into the Early Permian, and reaches up to 1,400 feet thick, composed mainly of sandstone and mudstone with secondary siltstone, limestone and conglomerate, its sandstones often cross-bedded and its limestones bearing red chert nodules; it divides, youngest to oldest, into the Esplanade Sandstone, Wescogame, Manakacha and Watahomigi Formations, recording repeated transgressive-regressive cycles. Its fossils are mostly marine invertebrates, chiefly brachiopods and pelecypods, with rarer vertebrate remains including xenacanth shark teeth and tetrapod trackways.