27

REGION 12: THE HIGH PLAINS

THIS region is characterized by an apparently perfectly level topography which, however, has an imperceptible slope to the south, and by a compact, finely textured dark-colored soil underlain at a depth of a few feet by a weather-resistant, naturally cemented stratum known as caprock. Erosion. by streams has cut through this stratum and through hundreds of feet of the softer soil beneath, creating the beautiful canyons that, besides the sinkhole lakes described below, constitute the only break in the otherwise utterly monotonous plain. Sometimes narrow, sometimes wide, with the cliffs which enclose their sinuous main and lateral branches always topped by the jagged, precipitous or over-hanging ledge of caprock, these canyons are surpassingly beautiful, with or without vegetational adornment. In this striking physical setting a number of factors combine to bring about an infinite variety of conditions which reflects itself in an equally infinite variety in the appearance of the vegetational covering. Such factors are the presence or absence of seepage water; the widely varying degrees and directions of slope-exposure combinations, with their concomitant favorable or unfavorable effect on vegetational growth; and the occurrence of protected, well-watered canyon heads or pockets.

The virgin cover of the level plains was originally composed of buffalo grass and various grama grasses, with Smith's Agropyron occupying the gentle slopes which border the sink-hole lakes. These, as the name indicates, are ponds of run-off water collected at the bottoms of shallow, basin-like depressions from which there is no outlet. Soil in this region has in general little or no alkali salts. The result is that the water in the lakes is fresh and entirely suitable for stock; there is no concentration of salts in the surrounding soil; and the consequent vegetation is not of the succulent type characteristic of saline localities. Slopes offer some protection against wind-sweep and give some opportunity for out-seep of soil water, so that growth conditions are more favorable on the basin sides than on level stretches. Colonel Goodnight told me that, in the