This region is characterized by flat and rolling plains with relief of less than 300 ft (90 m). Elevations range from 2,500 ft (760 m) near the western edge of the province to 1,000 ft (300 m) at the eastern edge. Except south of the Missouri River, most of the lands are young glacial drifts and dissected till plains. Water covers much of the surface. Loess and sand deposits cover the area south of the Missouri River. This flat-to-rolling hill land has well-developed drainage systems.

This region, called mixed-grass steppe, reaches from the tallgrass prairie parkland to the shortgrass steppe at about long. 104 W. As its name suggests, it contains a mixture of shortgrass and tallgrass species. Shorter dominants include blue grama, hairy grama, and buffalo grass. Taller grasses include little bluestem and needle-and-thread grass. Woody vegetation is rare, except on the cottonwood floodplains.