Geography of the Bluegrass & Nashville Basin
Ecoregions are groups of ecosystems with similar combinations of soils and land forms. While they are artifical (unlike, for example, watersheds), ecoregions are a convenient way to group and refer to similar landscapes. In the United States, Ecoregions are defined by the Environmental Protection Agency and its cooperators (read more about EPA Ecoregions here).
The Bluegrass and Nashville Basin are geographical regions wiithin the Interior Plateau ecoregion (Level III Ecoregions). The Interior Plateau consists of rolling hills interrupted by dissected upland, knobs, a few master streams and large areas of karst (erodable limestone). The rock beneath the Interior Plateau is largely limestone with calcareous shale, sandstone, siltstone and shale. Glacial activity is not present. Soils are predominantly alfisols. The natural vegetation of the Interior Plateau is hardwood forest, grasslands and canelands. Today, it consists of farmland and forest land, as well as a few large urban areas including Nashville, Louisville, Lexington and the southern suburbs of Cincinnati.
There are three Level IV ecoregions within the Bluegrass, the Inner Bluegrass, Hills of the Bluegrass and the Outer Bluegrass. The Hills of the Bluegrass are also called the Eden Shales. The Nashville Basin consists of the Inner and Outer Nashville Basin.
Although the Bluegrass and the Nashville Basin are formed from the same limestone feature, the Cincinnati Arch, they are very different topographically. Both are domes lifted up from the surrounding terrain, but the Nashville Basin was subsequently eroded below the uplifting Highland Rim. The elevation of the Inner Nashville Basin is from 550 to 650 ft, rising to a little over 1,000 ft. in the Outer Basin.
The elevation of the Inner Bluegrass is from 750-1065 ft, while the Hills of the Bluegrass and the Outer Bluegrass range from about 400 to 850 ft.