Miller County is located in the southwest corner of Arkansas in the
Piney Woods, a
temperate coniferous forest. The forests of pine trees initially formed a logging and
silviculture industry, though many fields have been cleared from the forest to grow rice, soybeans, corn, and vegetables. The county is also within the
Ark-La-Tex region, sharing a
tripoint with
Texas and
Louisiana. The Ark-La-Tex is an economic region anchored by
Shreveport, Louisiana,
Tyler, Texas,
Longview, Texas, and Texarkana. The
Red River serves as the northern and eastern boundary of the county, though the watercourse has shifted since the county's reestablishment in 1874. The original Red River continues to serve as the county line between Little River, Hempstead, and Lafayette counties in Arkansas. According to the
U.S. Census Bureau, Miller County has a total area of , of which is land and (2.1%) is water.
Ecology Miller County is within the
South Central Plains Level III ecoregion designated by the
Environmental Protection Agency. Within the region, the county contains parts of four different Level IV ecoregions. Throughout the South Central Plains, forests are mostly swamp - southern floodplain forest, unlike the oak–hickory–pine forest of higher, better drained forests in adjacent eco-regions. Along the north and eastern county boundary, the
Red River Bottomlands follows the Red River. This eco-region contains floodplains, low terraces, oxbow lakes, meander scars, backswamps, natural levees, and the meandering Red River. Natural vegetation is southern floodplain forest unlike the oak–hickory– pine forest of higher, better drained compared to adjacent forests. However, the region has widely been cleared and drained for agriculture. The Red River is almost continuously turbid; suspended sediment concentrations are usually much higher than in the
Saline River or
Ouachita River due to land cover, land use, and upstream lithology differences. 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.
Hydrology Miller County is within the
Red River watershed. The historic channel of the Red River defines the northern and eastern boundary of Miller County. Swamps and bayous along the Sulphur River drain much of the western part of Miller County. A levee in the eastern part of Miller County delineates the border between the McKinney Bayou watershed, with everything east of the levee within the Red River
floodplain. Areas within the levee are frequently subject to inundation by the Red, including a town evacuation of
Garland City in 2015.
Protected areas Miller County contains two protected areas: the Sandhills Natural Area owned by the
Arkansas Natural Heritage Commission (ANHC), and the Sulphur River
Wildlife Management Areas (WMA), owned by the
Arkansas Game and Fish Commission (AGFC). The Sandhills Natural Area preserves of undisturbed sandhill vegetation along rolling hills and sandy soils. It is a home to at least 40 rare species of plants, the most of any ANHC Natural Area. The Sulphur River WMA preserves of
bottomland hardwood forest,
cypress breaks,
oxbow lakes, and bayous along the Red River Valley. Established in the 1950s, the area is open to
birding, camping, hunting, fishing, and hiking. Within the WMA, is maintained as the Henry Moore Waterfowl Rest Area. ==Demographics==