South of Texarkana, the Floodplains and Low Terraces eco-region follows the Sulphur River. It contains frequently flooded forested wetlands, natural levees, swales, oxbow lakes, and meander scars. Longitudinal channel gradients are low and are less than in the Ouachita Mountains. North of the low terraces, a small strip of Pleistocene Fluvial Terraces ecoregion contains level, poorly-drained, periodically wet soils underlain by Pleistocene unconsolidated terrace deposits. Loblolly pine and oaks are common and are adapted to the prevailing hydroxeric regime; pastureland and hayland are less extensive. A vertical sequence of terraces occurs. The lowest terrace is nearly flat, clayey, and has extensive hardwood wetlands. Higher terraces become progressively older and more dissected; they are dominated by pine flatwoods, pine savanna, or prairie; flatwood wetlands are less extensive than on the lowest terrace. The mid-level terrace is veneered with windblown silt deposits (loess). Streams tend to be mildly acidic and stained by organic matter. They have more suspended solids, greater turbidity, and higher hardness values than the Tertiary Uplands.