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| This view of Kachina Bridge shows the ancient stream channel that was left high and dry after Armstrong Creek breached the promontory that now forms the bridge. This view also shows the slickrock upland surface that defines the top of the Cedar Mesa Sandstone. The steep, red slopes and dark cliffs in the distance consist of younger late Permian and Triassic formations. The bright red slope between the Cedar Mesa and the first dark cliff face is the Organ Rock Tongue of the Cutler Formation (about 300 feet or 90 meters thick). The lower, dark colored cliffs with narrow intervening slopes are the Moenkopi Formation. The Moenkopi consists of limestones and reddish sandstones, siltstones, and shales. Tracks of ancient reptiles and amphibians are preserved along with ripple marks and mud cracks in some layers of the Moenkopi. These trace fossils suggest that the sediments were deposited in shallow bays, mudflat's, marshes and the flood plains of broad, slow-moving streams in the early Triassic Period, about 240 to 230 million years ago. The top part of the Mesa consists of sandstones and shales of the Chinle Formation. Some layers of the Chinle Formation yields fossil wood, even fossil logs like those preserved in Petrified Forest National Park in Arizona. This fossil wood suggests that during periods of the Triassic Period, extensive lowland forested coastal swamps and river flood plains covered much of what is now the Colorado Plateau. In Permian to early Triassic time, low mountains or hills existed in the Western Colorado Region (geologists call these Ancestral Rocky Mountains and the Uncompahgre Uplift). These and other upland areas shed sediments into river systems that flow across the Colorado Plateau region into the Pacific Ocean basin. Some of these rivers may have flowed from as far away as the Appalachian Mountains or the Canadian Shield regions of North America and would have rivaled the Mississippi River in the volume of water and sediment transported across the continent. |
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