The Osage Plains are a physiographic section of the larger Central Lowland province, which in turn is part of the larger Interior Plains physiographic division. The area is sometimes called the Lower Plains, North Central Plains,or Rolling Plains. The Osage Plains, covering west-central Missouri, the southeastern third of Kansas, most of central Oklahoma, and extending into north-central Texas, is the southernmost of three tallgrass prairie physiographic areas. It grades into savanna and woodland to the east and south, and into shorter, mixed-grass prairie to the west. The Osage Plains consist of three subregions. The Osage Plains proper occupy the northeast segment. Although sharply demarcated from the Ozark uplift, the plains are nonetheless a transitional area across which the boundary between prairie and woodland has shifted over time. In the central portion of the physiographic area lies the second subregion, the Flint Hills, commonly called the Osage in Oklahoma. This large remnant core of native tallgrass prairie is a rocky rolling terrain that runs from north to south across Kansas and extends into Oklahoma. To the west and south of these hills are the Blackland Prairies and Cross Timbers. This vegetatively complex region of intermixed prairie and scrubby juniper-mesquite woodland extends into north-central Texas. Bluestem prairies and oak-dominated savannas and woodlands characterize the natural vegetation in the Cross Timbers. Much of the area has been converted to agriculture, although expanses of oak forest and woodland are still scattered throughout the eastern portion of the subregion.