The Ouachita Mountains, one of the six natural divisions of Arkansas,
are generally characterized as folded ridges and valleys composed of
Paleozoic rocks. They are unusual in North America in that the ridges
are generally aligned east to west, unlike the Rocky Mountains or
Appalachian Mountains, where the ridges usually run north to south.
The most striking result of this orientation is that there is an
extensive south-facing slope on each ridge that is exposed to the heat
and light of the sun, as well as a north-facing slope that is
protected from direct solar radiation and is consequently cooler and
moister. The dry south-facing slopes are often covered with pine
forests or woodlands, or even drier oak woodlands, while the moister
north-facing slopes are covered with diverse hardwood forests. This
results in distinct east-to-west bands of vegetation that can be seen
from an airplane or by satellite. The bands usually shift repeatedly
from pine forest to hardwoods and back, moving from north to south.
This is particularly apparent in the winter when the green color of
evergreen pines contrasts dramatically with the brown of the leafless
deciduous hardwoods.