BAD LANDS, a term originally applied to certain areas in western South Dakota which, because of their extreme roughness and inhospitability to man, were called Maka Sicha (maka, bad; sicha, lands) by the Dakota Indians, Mauvaises Terres by the French Canadian trappers of the region, and later "bad lands" by the white settlers. More recently the term has come to have only a topographic significance and is applied to regions sharing characteristics of the type area—the White river region of South Dakota. Other areas of bad lands occur in North Dakota, Ne braska, Montana, Wyoming, Colorado. New Mexico, Arizona, Utah and other Western States and in various regions of other conti nents, notably South America and Asia.
The South Dakota bad lands are still known as the most pic turesque and rugged areas of their kind in the world. They are variously known as the White River Bad Lands, the Big Bad Lands or even the Bad Lands.
Typical bad lands are areas intimately dissected by running water into innumerable, winding, narrow, steep-sided gullies sepa rated by narrow, serrate divides. They are found fringing the outer valley walls of some master stream to which the gullies are tributary or in a zone bordering table-lands that lie a few hundred feet above the general level of the surrounding country. The width of the dissected area varies considerably but seldom ex ceeds a few miles. In depth, the gullies usually vary from a few tens of feet to a few hundred feet. Gradients of stream courses in the valley bottoms are normally high, increasing toward their sources, where they may become nearly, if not quite, vertical. On the side-walls there are many alternations of steep slopes, pro jecting ledges and more gentle slopes. Divides between gullies are narrow, tortuous in direction and are interspersed with pin nacles and sags. Isolated peaks, pillars and pulpit rocks capped by more resistant portions of rock abound. The coalescing of gullies frequently leaves isolated flat-topped buttes, pyramidal or conical-shaped hills or wedge-shaped short ridges.
Viewed from the valley of the master stream to which the dis secting gullies are tributary, the fringe of bad lands appears against the sky-line much as a sawtooth mountain range appears from a greater distance. From the upland area one may approach the bad lands over level country with no hint of their presence until the head of a ravine is reached, when the whole intricate maze of gullies, ridges and peaks is seen suddenly.
Origin.—Bad lands are chiefly the result of the erosive work of running water. Erosion by the wind, the dissolving action of underground water and other agencies may play a part in the shaping of some forms, e.g., by the etching out of the less resistant portions of rock, but these are merely incidental to the cutting of gullies.
For the formation of bad lands three factors seem to be the determinants : the nature of the underlying rock material; (2) the gradient or slope of the land surface; (3) the climate of the region.
The most favourable rock material is a fine-grained, poorly cemented one of low permeability to water, such as clay or soft shale with perhaps some friable, fine sandstone or volcanic ash. When moistened, many of these clays expand and when dried may curl up in flakes and spring loose from the underlying mass or they may swell into spongy masses and dry in loose, incoherent aggregates resembling cauliflower heads. Such material is readily removed by slope wash during successive rains. The fineness of the material facilitates rapid transportation so that the chances for accumulation or deposition are small so long as water is flowing over the surface.
Stratified clays and shales are often alternately interbedded with sandstones, conglomerates, limestones or other more re sistant layers. Shales, furthermore, often contain hard spherical concretions that may offer greater resistance to removal. Erosion of such material results in isolated resistant masses such as concre tions or conglomerate boulders and gives rise to pillars of clay capped by these harder rocks. Pulpit rocks, toadstool rocks and like forms capped by slabs of sandstone or limestone are f ormed in a similar manner.
In bad lands the down cutting action of streams dominates over the side cutting. In order that this may take place the gradient of stream valleys must be steep. In many cases steep gradients are made possible by the rapid excavation of a large valley by a master stream which heads in some region of more abundant rainfall and which erodes its valley more rapidly than the tributaries from the bad lands areas where there is less rainfall.
The climate of regions of bad lands is mostly arid or semi arid. Daily as well as yearly variations in temperature are great. Humidity is low. Rainfall is likely to be concentrated in heavy showers within short intervals alternating with longer periods of drought. During the sudden downpours of rain, slopes are washed clean of the fine clays loosened during the preceding period of moistening and drying, and any small vegetation that may have gained a foothold is quickly swept away. The great concentration of water from the bare side slopes rushes down the gullies, removing material from the bottom, and deepens the trenches.
Life.—In the bad lands proper there is little vegetation of any kind partly because of the deficiency of rainfall, but largely be cause of the difficulty plants have in maintaining a foothold under the severe conditions of erosion. Animal life in the bad lands is likewise scarce because of the meagre supply of plant food. A few birds, an occasional rabbit, gopher, prairie-dog, mouse, snake or coyote are likely inhabitants of such a region.
Fossils.—The rock formations of bad lands probably con tain fossils in not greater abundance than the rocks of other regions, but the bare slopes and the rapid erosion make f ossil finding in these areas easier. Among the fossils found are those of the horse, camel, rhinoceros, dog, cat, tapir, deer, rodent, insect eater, turtle, crocodile, eggs of birds and the remains of many animals now extinct.