The Central Lowlands and Great Plains
Vance T. Holliday
James C. Knox
Garry L. Running IV
Rolfe D. Mandel
C. Reid Ferring
The Central Lowlands and Great Plains represent the stable interior of North America south of the Boreal Forest (fig. 17.1). The two regions comprise the vast low-relief landscape between the Appalachian-Ouachita mountain system on the east and southeast, and the Rocky Mountains and eastern Basin and Range Province on the west. Most of the Central Lowlands are below 600 m above sea level and substantial segments are lower than 300 m. The Great Plains, drier and higher than the Lowlands, reach elevations between 600 and 1800 m. The Central Lowlands and Great Plains are stereotypically characterized as environmentally, topographically, and geologically homogeneous if not monotonous. As shown subsequently, however, these regions possess considerable physiographic diversity.
The bedrock of the Central Lowlands and Great Plains consists mostly of terrestrial and shallow marine sedimentary material representing most of Phanerozoic time (Sloss, 1988; Stott and Aitken, 1993). In the Central Lowlands, the Paleozoic and Mesozoic rocks become generally younger to the south and west away from the Precambrian crystalline cratonic core of the continent exposed toward their northern margin. Some variation in the outcrop pattern is imposed by large-scale Paleozoic structures such as the Michigan and Illinois Basins and the Cincinnati and Wisconsin Arches in the northeastern Central Lowlands, the Anadarko Basin in the southern Central Lowlands, and the Williston Basin in the northern Great Plains (fig. 17.1) (Sloss, 1988; Bally, 1989). Lower Paleozoic rocks, more common in the northern Central Lowlands around the Great Lakes, are mostly marine sediment, usually limestone or shale. Upper Paleozoic rocks are more common in the southern half of the Central Lowlands and include both terrestrial deposits, typically sandstones and evaporites, and marine deposits, including limestones and shales.
Mesozoic deposits are most common along the western margin of the Central Lowlands and throughout the Great Plains. These deposits are mainly Cretaceous limestones and terrestrial clastics. Though often eroded or buried beneath the High Plains, these rocks are ubiquitous at or near