Within the Great Plains are many large areas that differ greatly from adjoining areas (fig. 3). The Black Hills stands out distinctively from the surrounding lower land, and its dark, forested prominence can be seen for scores of miles from any direction. At the southern end of the Great Plains is another, less imposing, forested prominence—the Central Texas Uplift. Most impressive, perhaps, is the huge, nearly flat plateau known as the High Plains, which extends southward from the northern border of Nebraska through the Panhandle of Texas, and which forms the central part of the Great Plains. The east and west rims of the southern High Plains are at high, cliffed, erosional escarpments—the Caprock escarpment on the east and the Mescalero escarpment on the west. The north edge of the High Plains is defined by another escarpment, the Pine Ridge escarpment, which separates the High Plains from a region that has been greatly dissected by the Missouri River and its tributaries. There, several levels of rolling upland are surmounted by small mountainous masses and flat-topped buttes and are entrenched by streams. This region is the Missouri Plateau. The continental glacier lapped onto the northeastern part of the Missouri Plateau and altered its surface. The South Platte and Arkansas Rivers and their tributaries have similarly dissected an area along the mountain front that is called the Colorado Piedmont, and the Pecos River has excavated a broad valley trending southward from the Sangre de Cristo Mountains in New Mexico into Texas. The Mescalero escarpment separates the Pecos Valley from the southern High Plains (fig. 4). South and east of the Pecos Valley, extending to the Rio Grande and the Coastal Plain, is a broad plateau of bare, stripped, flat-lying limestone layers bearing little but cactus that is called the Edwards Plateau. Green, crop-filled valleys with gently sloping valley walls and rounded stream divides trend eastward from the High Plains of western Kansas and characterize a Plains Border section. And finally, between the Colorado Piedmont on the north and the Pecos Valley on the south, volcanic vents, cinder cones, and lava fields form another distinctive terrain in the part of the Great Plains called the Raton section. [Illustration: _Figure 3.—The Great Plains province and its sections._] [Illustration: _Figure 4.—Mescalero escarpment and the southern High Plains (Llano Estacado) south of Tucumcari, N. Mex., Photograph by C. D. Miller, U. S. Geological Survey._]