The Coastal Plain
Although called a plain, the Coastal Plain has a wide variety of landscapes. In places it is a flat, relatively featureless plain, but elsewhere it consists of rounded and eroded hills, cuestas and flatwoods, and the floodpains of the Alabama, Black Warrior, Cahaba, Tombigbee and Chattahoochee rivers.
Eight districts occur in this section (Figure CPD1)
Figure CPD1. Physiographic districts of the Coastal Plain. AP: Alluvial-deltaic Plain, BP: Black Prairie, CH: Chunnenuggee Hills, DP Dougherty Plain, FLH: Fall Line Hills, LH: Lime Hills, SPH: Southern Pine Hills, SRH: Southern Red Hills. Broken black lines: topographic profiles. Black circles N to S: Montgomery, Mobile. (National Map Viewer, USGS and Geological Survey of Alabama)
Relationship of Physiographic Districts to Geology:
Locally, higher elevations are underlain by more-resistant material, in some cases sediment, in others rock, and the lowlands are underlain by softer material. The type of resistant material varies from one physiographic district to another.
Roughly northwest-southeast trending cuestas with intervening flatwoods are the distinctive features of most of the coastal plain. The north-facing slope of each cuesta is steeper than the southerly slope, which represents the dip of the underlying beds. Between cuestas are valleys (often called flatwoods) that tend to be a distorted “V” shape in profile, with a gentler northern slope and a steeper southern slope. Local relief (elevation difference between top of cuesta and flatwoods floor) is up to 300 feet (Figure CPD2).
Figure CPD2. Idealized topographic profile across and cuestas and flatwoods. Brown: contacts between beds of sediment or rock .
Each cuesta is capped by more-resistant material, in some cases it is sediment, in others rock, and the flatwoods is cut in the locally softer material. The type of material capping cuestas varies from one physiographic district to another.