The underlying bedrock in the Glaciated Region is Pennsylvanian and
Permian limestones and shales that dip gently to the west and northwest.
These rocks, however, have been covered by thick glacial deposits--silt,
pebbles, and boulders--that were left behind when the ice melted. In
some places, the thick deposits, which geologists call glacial drift,
have formed deep soils.
Except for the glacial drift, most of the evidence of glaciation has
been erased from the Kansas landscape by erosion. In other parts of
North America, such as Wisconsin, the glaciation was more recent and
the landscape still bears the marks of the advancing and retreating
ice sheet.
During the Pre-Illinoian glaciation in Kansas, the force of the advancing
ice was strong enough to break large boulders off outcrops in South
Dakota, Iowa, and Minnesota and carry them into Kansas. Reddish quartzite
boulders, known as Sioux quartzite, are common throughout the region.
Osage
Cuestas
The
Osage Cuestas region occupies nearly all of eastern Kansas south of
the Kansas River and is characterized by a series of east-facing ridges
(or escarpments), between hich are flat to gently rolling plains. Cuesta,
Spanish for hill or cliff, is the term geologists use to describe ridges
with steep, clifflike faces on one side and gentle slopes on the other.
In the Osage Cuestas, the underlying strata are Pennsylvanian limestones
and shales that dip gently to the west and northwest. Each cuesta consists
of a striking east-facing ridge or escarpment and a gently inclined
surface that slopes in the direction of the dip of the strata. Each
escarpment is capped by the more-resistant limestone, while the gentle
slopes are underlain by thick layers of shale. The steep faces of the
cuestas range in height from approximately 50 feet to 200 feet.
Flint
Hills
The
Flint Hills are familiar to many travelers since this part of the state
is traversed by both I-70 and the Kansas Turnpike. Despite disagreement
about the exact boundaries of the Flint Hills, most geologists agree
that the hills extend from Marshall County, in the north, to Cowley
County, in the south. (Of course, the hills don't end abruptly at the
state line; they continue into Oklahoma, where they are known as the
Osage Hills.)
The Flint Hills were formed by the erosion of Permian-age limestones
and shales. During the early part of the Permian Period (which lasted
from about 286 to 245 million years ago) shallow seas covered much of
the state, as they did during Pennsylvanian times. Unlike the Pennsylvanian
limestones to the east, however, the limestones in the Flint Hills contain
numerous bands of chert, or flint. Because chert is much less soluble
than the limestone around it, the weathering of the limestone has left
behind a clayey soil full of cherty gravel. This gravel-filled soil
covers the rocky uplands and slows the process of erosion. Most of the
hilltops in this region are capped with this cherty gravel.
Because of the cherty soil, the land is better suited to ranching than
farming. Because of this, the Flint Hills is still largely native prairie
grassland, one of the last great preserves of tallgrass prairie in the
country.
The tall grasses in this region are mostly big and little bluestem,
switch grass, and Indian grass. Except along stream and river bottoms,
trees are rare. The streams in the Flint Hills have cut deep precipitous
channels. Streams cut in chert-bearing strata are narrow, boxlike channels,
whereas those cut in weaker shales are wider, more gently sloping valleys.
Smoky
Hills
The
region known as the Smoky Hills occupies the north-central part of the
state. It is delineated by outcrops of Cretaceous-age rocks and takes
its name from the early morning haze that often gathers in the valleys.
During the Cretaceous Period (that interval of geologic time from about
144 to 66 million years ago), Kansas was once again under water. Unlike
the relatively shallow seas of the Pennsylvanian and Permian, the seas
that advanced and retreated during the Cretaceous were deeper and more
widespread. Three principal rock outcrops characterize the Smoky Hills--the
sandstones of the Dakota Formation, the limestones of the Greenhorn
Limestone, and the thick chalks of the Niobrara Chalk.
The Dakota Formation sandstones crop out in a wide belt from Rice and
McPherson counties, in the south, to Washington County, in the north.
They are the remains of beach sands and sediments dumped by rivers draining
into the early Cretaceous seas. The hills and buttes in this part of
the Smoky Hills, such as Coronado Heights in Saline County, are capped
by this sandstone and rise sharply above the surrounding plains.
The next outcrop belt to the west is the Greenhorn Limestone, which
is made up of thin (usually less than 6 inches) chalky limestones beds
alternating with thicker beds of grayish shale. The Greenhorn Limestone
was deposited in a relatively shallow part of the Cretaceous sea. Near
the top of the Greenhorn is a limestone bed called Fencepost limestone.
Because timber was scarce in this part of the state, limestone was used
extensively by early settlers for buildings and fenceposts.
The third and westernmost range of hills in the Smoky Hills developed
on the thick chalks of the Niobrara Chalk. These chalk beds, which were
deposited in the deeper part of the Cretaceous ocean, are exposed in
bluffs of the Solomon, Saline, and Smoky Hill rivers and in an irregular
belt from Smith and Jewell counties to Finney and Logan counties. The
Niobrara is known for the pinnacles, spires, and odd-shaped masses formed
by chalk remnants, such as Castle Rock and Monument Rocks in Gove County.
It is also known for fossils of swimming reptiles such as plesiosaurs
and mosasaurs that lived in the ocean while dinosaurs roamed the land.
High
Plains
In
Kansas, the High Plains region comprises almost all of the western one-third
of the state. It is an area of vast flatlands and gently rolling hills,
with topographic relief largely restricted to streams and river valleys,
such as the Arikaree Breaks in Cheyenne County or along the Cimarron
River in Seward County.
The High Plains developed on sediments that originated in the Rocky
Mountains to the west. The Rocky Mountains were formed by deformations
of the earth's crust at intervals during the last part of the Cretaceous
Period and continuing into the Tertiary Period, which lasted from approximately
66 million to 1.6 million years ago. By late Tertiary time, just a few
million years ago, the Rockies were being eroded by wind and water.
Streams flowing eastward out of the Rocky Mountains were full of sand,
gravel, silt, and other rock debris. Over millions of years, this mass
of eroded material filled the stream valleys and eventually covered
the hills, creating a huge, gently sloping floodplain. The remnants
of that region (which extends far beyond the Kansas border) is the region
we call the High Plains.
The great wedge of sand and gravel that lies below the surface is the
Ogallala Formation. The Ogallala is made up of the unconsolidated deposits
(sands, gravels, clays, and other materials) that eroded off the face
of the Rockies. Some of this material was cemented together to form
porous sandstones, which are known as mortar beds. Most of the Ogallala
is underground, but it crops out in many places, such as at Scott County
State Lake. The Ogallala is one of the chief sources of ground water
in western Kansas.
The High Plains get less precipitation than other parts of the state,
averaging between 15 and 25 inches a year. The combination of low precipitation,
windiness, and abundant sunshine makes for a dry, or semiarid, climate
in much of the High Plains. Short, drought-tolerant grasses cover the
uncultivated areas, trees are scarce, and desert-type plants, such as
cactus and yucca, are common.
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