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Arkansas's Natural Regions
Arkansas has two well-defined natural regions. A line drawn from the
northeastern corner of the state southwestward through Little Rock to
Arkadelphia, and from there due west to the Oklahoma border, separates the two
regions. North and west of the line are the Interior Highlands; east and south
of the line is the Coastal Plain.
The Interior Highlands include the Ozark Mountains, the Ouachita Mountains, and
the Arkansas River Valley, which divides the two highland regions. The highest
mountain peak in the state, Magazine Mountain, rises abruptly from the Arkansas
Valley floor to 839 m (2753 ft) above sea level. Other isolated peaks in the
valley are Sugar Loaf Mountain, Poteau Mountain, Mount Nebo, and Petit Jean
Mountain.
North of the Arkansas Valley are the Ozark Mountains, or Ozark Plateaus, which
lie mainly in southern Missouri. Commonly known as the Ozarks, they are made up
of ancient sandstones and limestones. In many places the limestone has been
dissolved by water to form caves, sinks (depressions or holes in the earth's
surface), and even underground river channels. The southern part of the Ozarks
is known as the Boston Mountains, which extend about 300 km (about 200 mi) from
east to west. They form the most rugged part of the Ozarks and are bounded on
the north by a gentle escarpment. With peaks more than 700 m (2300 ft) high, the
Boston Mountains are a heavily wooded tangle of steep sandstone ridges and
jagged spurs, cut through by gorges as much as 430 m (1400 ft) deep.
South of the Arkansas Valley are the Ouachita Mountains, which also contain
rocks of great age. The rock layers here were subjected to tremendous pressure
in the geologic past and were pushed into folds that now form long, narrow
ridges that run from east to west and are separated by wide basins. The
Ouachitas cover a belt about 80 to 100 km (about 50 to 60 mi) wide extending
from just west of Little Rock into Oklahoma. They rise to the west, reaching
over 800 m (2600 ft) at Blue Mountain near the Oklahoma state line.
The Coastal Plain in Arkansas extends across the eastern and southern parts of
the state in two sections. The easternmost section is composed of the fertile
Mississippi Alluvial Plain. This is often called the Delta, and until it was
cleared for agriculture it was an area of swamps, dense forest, and tangled
undergrowth. Its flat expanse is broken only by a narrow strip of hills, called
Crowley's Ridge, which extends about 240 km (about 150 mi) from Helena on the
Mississippi River north to the Missouri border where it reaches a height of
about 170 m (about 550 ft). West of the southern part of the Delta is the West
Gulf Coastal Plain, drained by the Saline, Ouachita, and Red rivers.
Rivers and Lakes
Abundance of water is a distinctive feature of Arkansas. The entire state drains
southeastward to the Mississippi River, which forms the eastern boundary of
Arkansas. There the Mississippi flows and winds its way across a wide
floodplain.
The Arkansas River is a major tributary of the Mississippi River. It rises as a
small stream in the Rocky Mountains, and by the time it reaches Arkansas it is a
great river flowing between broad banks. The water level on the river fluctuates
seasonally. Other major rivers of the state are the Red River, which forms part
of the boundary with Texas; the Ouachita River and its tributary, the Saline,
which drain south-central Arkansas; the White River and its tributaries, the
Black and the Little Red, which gather the runoff of northern Arkansas; and the
Saint Francis River, in the northeast, which flows almost parallel to the
Mississippi before joining it near Helena.
There are no large natural lakes in Arkansas. The largest bodies of water are
reservoirs behind dams. Among the larger of these lakes are Beaver and Greers
Ferry reservoirs, Bull Shoals Lake, and Lake Norfolk, all of which are located
on the White River or its tributaries; Ozark Reservoir and Dardanelle and Nimrod
lakes, all on the Arkansas River or its tributaries; Lake Ouachita, on the
Ouachita River, Lake DeGray, on the Caddo River; and Millwood Reservoir, on the
Little River, which is a tributary of the Red River.
Climate
Arkansas's Climate
Temperature
Except in the Ozark and Ouachita uplands, where temperatures vary considerably
from ridge to valley, the climate throughout Arkansas is fairly uniform. Summers
are long and moderately hot, and winters are short and relatively mild. However,
northward and westward from the Coastal Plain, there is a gradual change from
warm winters and hot, humid summers to the clearer, brisker, drier weather and
wider range of temperatures associated with the Interior Plains. January
temperatures in most of Arkansas average between 38° and 46° F. July averages
are between 78° and 82° F throughout most of the state. They are usually in the
upper 70°s F in the Ozark and Ouachita uplands. Daytime highs in July are
frequently in the middle 90°s F and sometimes the temperature rises to the lower
100°s F.
Precipitation
Arkansas receives about 40 to 50 in of precipitation a year, and some areas
receive even more. Most of the rain comes during winter and spring and at times
is so heavy as to cause flooding. Snow is rare in the south but amounts to more
than 10 in a year in the mountains. |
