Region 10: Sotol-Lechuguilla
PERHAPS on the principle of first impressions being the most lasting, the image which comes most vividly to mind upon the mention of Trans-Pecos for those who know the country, is one of roughly rolling, high and rocky hills covered with a dense growth of sotol and lechuguilla; for this is what one beholds for miles from Del Rio to the Pecos and beyond. But these plants neither dominate the region indicated as 10 on the map, nor are they by any means absent from the mountainous regions—designated as B—which rise above the general altitude to form the various ranges. In fact they are as prominent a vegetation type on the lower, sloping, mountain ridges as they are on the foothills and sub'foothills leading up to the mountains.
Northward, and mostly beyond the Pecos, mesas rise conspicu ously above the intervening valleys. Their flat tops, formed by weather-resistant fragments of the Plains caprock, frequently over hang the softer underlying strata; and around the edges cacti, Acacia, Mimosa, Fouguiera, Condalia, and other thorny shrubs abound. Sotol and lechuguilla cover the slopes in many places. Intervening broad level "valleys'" are covered with semi-desert grasses—burro, squirrel-tail, Muhlenberg, tobosa, and galleta, with buffalo, curly mesquite and the gramas in the better watered portions near stream ways—and scattered xeric 12 shrubs; or, on gravelly clay and somewhat saline soils, a mixture of creosote bush and Flourensia (a yellow composite) makes a conspicuous shrubby cover.
The latter type of vegetation is common also in foothills and broad inter-mountain valleys northward and westward to Utah and Arizona.
Over great stretches of country from the Pecos river to Sanderson the characteristic vegetation is the famous purple sage Cenizo (Leucophyllum texanum), a gray-leaved shrub which bursts into
12 Xeric, implies adaptation to a dry habitat.