Sideoats grama (Bouteloua curtipedula) is the official State Grass of Texas, found in every bioregion in the state.
The Rolling Plains region, together with the High Plains region, is the southern end of the Great Plains of the central United States. Topography is gently rolling to moderately rough and dissected by narrow intermittent stream valleys flowing east to southeast. Elevation is 800 to 3,000 feet. The eastern portion is sometimes known as the Reddish Prairies. Annual rainfall ranges from 22 inches in the west to nearly 30 inches in the eastern portion. May and September usually are high rainfall months. A summer dry period with high temperatures and high evaporation rates is typical. Soils vary from coarse sands along outwash terraces adjacent to streams, to tight clays or red-bed clays and shales. Soil reaction is neutral to slightly alkaline.
The region is bordered on the west by the Caprock Escarpment, on the south by the Edwards Plateau, and on the east by the Western Cross Timbers and Lampasas Cut Plain.
The original prairie vegetation included tall and midgrasses such as bluestems and gramas. Buffalo grass and species of three-awn, among others, tend to increase under grazing. Mesquite is a common invader on all soils. Shinnery oak and sand sage increase or invade on the sandy soils. Stream floodplains are dominated by various hardwood species. Juniper clings to the steep slopes along rivers.
The original prairie vegetation included tall and mid-grasses, such as little bluestem, big bluestem, sand bluestem (Andropogon Hallii,) side-oats grama, Indiangrass, switchgrass, hairy grama, blue grama, Canada wild-rye and western wheatgrass (Agropyron Smithii). Buffalograss, curlymesquite, tobosa (Hilaria mutica) species of three awn (Aristida spp.), sand dropseed, hooded windmill grass (Chloris cucullata) and Cenchrus species tend to increase under grazing. Mesquite is a common invader on all soils. Shinnery oak (Quercus Havardii ) and sand sage (Artemisia filifolia) increase or invade on the sandy lands. In addition to brush invaders, heavy grazing tends to increase sandburs (Cenchrus spp.), hairy tridens, red grama, Texas grama, tumblegrass, gummy lovegrass (Eragrostis curtipedicellata) Texas croton (Croton texensis), western ragweed and many other annuals and weedy perennials.
There are three subregions: the Mesquite Plains, Escarpment Breaks, and the Canadian Breaks. The Mesquite Plains subregion typifies the Rolling Plains Region. It is a gently rolling plain of mesquite-short grass savanna. Oak, cedar, acacia, and mimosa are important secondary elements of the brush portion on the savanna. Steep slopes, cliffs, and canyons occurring just below the edge of the High Plains Caprock comprise the Escarpment Breaks subregion. The Breaks are an ecotone or transition zone between the High Plains grasslands and the mesquite savanna of the Rolling Plains. Brush species including junipers, buffalo currant, and joint-fir dominate the vegetation of this subregion. The Canadian Breaks subregion is similar to the Escarpment Breaks, but also includes the floodplain and sandhills of the Canadian River in the northern Panhandle, bounded north and south by the edge of the Caprock. It is a mixed grass prairie with some low shrubs grading from succulents and dwarf shrubs in the east to shinnery, a savanna or groveland of scattered clusters of woody species, in the west.