The Missouri Plateau, the Colorado Piedmont, the Pecos Valley, and the
Edwards Plateau all were outlined by streams that flowed from the
mountains. On the eastern border of the Great Plains, however, headward
cutting by streams that have their source areas in the High Plains has
dissected a large area, mainly in Kansas. This Plains Border Section
comprises a number of east-trending river valleys—of the Republican,
Solomon, Saline, Smoky Hill, Arkansas, Medicine Lodge, Cimarron, and
North Canadian Rivers—and interstream divides, most of which are
intricately dissected.
North of the Arkansas River, the east-flowing Republican, Solomon,
Saline, and Smoky Hill Rivers have incised themselves a few hundred feet
below the Tertiary High Plains surface and have developed systems of
closely spaced tributary draws. The interstream divides are narrow, and
the tributary heads nearly meet at the divides. This intricately
dissected part of the Plains Border section is called the Smoky Hills.
Some isolated buttes of Cretaceous rocks left in the upper valley of the
Smoky Hill River are called the Monument Rocks. A large area of rounded
boulders exposed by erosion south of the Solomon River, southwest of
Minneapolis, Kans., is called “Rock City.” These boulders originated as
resistant nodules (concretions) within the Cretaceous rocks that
contained them.
South of the Arkansas River is a broad, nearly flat upland sometimes
referred to as the Great Bend Plains. The Medicine Lodge River has cut
headward into the southeastern part of the Great Bend Plains and created
a thoroughly dissected topography in Triassic red rocks that is locally
called the Red Hills. In a few places, badlands have formed in the Red
Hills.
Some large sinks or collapse depressions have formed because of solution
of salt and gypsum at depth by ground water. Big and Little Basins, in
Clark County in south-central Kansas, were formed in this way.
Sand dunes have accumulated in places, especially near stream valleys.
Dunes are common, for example, along the north side of the North
Canadian River.
Oil and gas fields are widely developed in the southeast part of the
Plains Border section—in the Smoky Hills, the Great Bend Plains, and the
Red Hills.
The Plains Border section, like the Missouri Plateau, the Colorado
Piedmont, and the Pecos Valley, is primarily a product of stream
dissection. The differences in the outstanding landforms of the section
are mainly the result of differences in the hardness of the eroded
rocks.