Novice geologists who visit a region such as the Permian Basin of West Texas might be surprised to find that the area does not resemble a broad valley. Geologic basins refer to the shape of the deep sediment formations and to their deposition in a structural bowl of ancient Precambrian or early Paleozoic bedrock. In the case of the Permian Basin, a thick layer of Permian sea sediments collected within such a basin; now covered over by Mesozoic and Cenozoic strata (which have been sculpted into the West Texas landscape by wind and water erosion) the deeper Permian rocks are tapped for their rich oil and gas deposits.
Further north, the Michigan Basin is often confused with the glacial-carved basin of Lake Michigan (a shallow surface feature). Rather, centered over Lower Michigan, this geologic basin extends from western New York to eastern Wisconsin and from Upper Michigan to northern Ohio. This broad bowl of Precambrian bedrock has gradually filled in with Paleozoic and Mesozoic sediments; as layers were added over a span of 400 million years, the basin closed in from the periphery and the youngest deposits (Jurassic in age) lie in the central part of Lower Michigan. Lakes Michigan, Erie and Huron, the varied topography of Michigan and Niagara Falls are all erosion-produced surface features of the Basin.
In northeastern Wyoming and southeastern Montana, the Powder River Basin is famous for its vast supply of low-sulfur coal. Derived from swamplands of the late Cretaceous and early Tertiary Periods, this coal is near the surface of a wide geologic basin that underlies the region and includes deposition layers that date back to the Precambrian Era. Unlike the other examples discussed above, Powder River is also a topographic basin, a broad valley that has been eroded from the surrounding landscape by the River and its tributaries; indeed, this erosion of soft, overlying Tertiary deposits has made the Powder River coal especially accessible.
