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270
Origin of Kaibab Formation
This formation originated during the Permian period and consists of a mixture of light gray to tan sandstone and limestone, as well as chunks of brown chert. It probably formed under a shallow ocean as many fossils of marine animals are present in these strata -
Period: 270 to
Time in millions of years before present day
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275
Origin of Toroweap Formation
The Toroweap Formation is a complex mixture of at least a half a dozen distinct mineral types, including sandstone, pink shale, redbed shale, gypsum, limestone, dolomite, and halite (salt crystals). Like the Kaibab formation, it bears fossils of marine animals but less richly than the Kaibab. It formed during the Permian period probably as a shallow sea began encroaching upon the area. -
325
Origin of Supai Group
Like the later Toroweap Formation, the reddish Supai Group is a complex mixture of minerals, including sandstone, siltstone, shale, limestone, and chunks of jasper (red chert). Also like the Toroweap, the Supai was probably a seashore sedimentary deposit, although wind might have been responsible for some of the deposit. The Supai began forming during the Pennsylvanian period. -
340
Origin of Redwall Limestone
Also called the Temple Butte Formation, this grayish limestone was dyed a vivid red by iron oxide depositions. Like most limestone, it probably formed deep beneath the ocean as many marine invertebrate fossils are present in the strata. There is also evidence in these strata of considerable subsidence (dropping of the sea floor) during this time (the Mississipian period). -
505
Origin of Muav Limestone
This formation, formed during the Cambrian period, is actually a yellow-gray mixture of limestone and shale. It was most likely a deep sea deposit as numerous fossils of invertebrate trackways, trilobites, brachiopods, and other mollusks are present -
510
Origin of Bright Angel Shale
This attractive gray-green rock is a mixture of shale and sandstone. Like the Muav Limestone just above it, it was probably a deep sea formation. It has an especially rich fossil record, including trilobites, brachiopods, and other primitive mollusks. It formed during the Cambrian Period. -
515
Origin of Tapeats Sandstone
This brownish sandstone has a distinctive conglomerate base with schist and granite pebbles embedded within it. It probably represented the last gasp of an ancient continent or island chain as it was worn flat by ocean waves. It formed during the Cambrian period. -
Probable origin of Vishnu Complex rocks
The Colorado River is presently cutting its way through the Vishnu basement rock layers. These incredibly ancient Precambrian rocks consist of schist layer intruded by granite dikes. Some of the granite has been metamorphosed into gneiss. The presence of the gneiss indicates tectonic activity that may have resulted in the building of a mountain or island chain and perhaps volcanic activity as well. Over time, the mountains or islands were eventually worn flat by erosion. -
Origin of Coconino Sandstone
This tan to white colored sandstone bears fossil trackways of invertebrates and early reptiles. It formed during the Permian period when the region was probably covered by a desert -
Origin of Hermit Formation
This reddish formation consists of a mixture of shale, siltstone, and sandstone. The fossil record in these strata include invertebrate trackways, worm burrows, and various plants including ferns and coniferous trees. It was probably deposited by a river during the Permian period as the land was beginning to dry out into a desert.
