38 GUIDEBOOK OF THE WESTERN UNITED STATES 
thickets of palmetto (Sabal glabra). On the slightly higher slopes are 
heavy forests of longleaf and loblolly pines. At Houston, still on 
the Coastal Plain, the sand ridges are higher and many of them are 
forested with pine, but the western limit of this tree is soon reached. 
The prairies with wet-soil grasses have rushes, sedges, and many 
prairie annuals. Here the rainfall is about 45 inches. In the next 
hundred miles a rolling upland 300 to 400 feet high is traversed, with 
sandy ridges and rich alluvial bottoms. There is much grass land, 
abundant clumps of post oaks, scattered live oaks, and many sandy- 
soil species, besides several cacti of the “pricklypear” character, 
called ‘‘nopal”’ by the Mexicans. The rainfall is about 35 inches a 
year. About San Antonio, 316 miles west of the Sabine River, near 
the inner margin of the Coastal Plain, where the elevation has 
increased to 500 to 700 feet and the annual rainfall has decreased to 30 
inches, the change in vegetation is very marked. Here the mesquite, 
huisache, cactus, zizyphus, yucca, and acacia, with many dry-soil 
grasses and annuals, are prevalent. On the Edwards Plateau, not 
far northwest, there is much small timber comprising numerous 
junipers, mountain live oak (encino), hackberry, shin oak, cedar elm 
(Ulmus crassifolia), and a few northern and Sonoran types, notably 
madrofio (Arbutus xalapensis). 
Near Spofford and Del Rio the western portion of the Rio Grande 
Plain is crossed. Its elevation is about 1,000 feet, and the annual 
rainfall averages 20 inches. Its surface consists of wide plateaus and 
low rolling ridges covered with gravel, sustaining much chaparral 
east. The average height of woody growth also is much reduced. 
Mesquite predominates, but there are many other plants characteris- 
tic of semiarid regions. The creosote bush (Covillea tridentata) begins 
and from this region into California is a prominent member of the 
flora in many places. Cacti are more abundant, and the grasses are 
mostly in bunches. From a point near Langtry to and beyond San- 
derson plateau topography prevails, with elevations of 1,300 to 2,000 
feet, and the rainfall is about 15 inches. There is great development 
of sotol (Dasylirion texanum), lechuguilla (Agave lechuguilla), covillea, 
yueea, the allthorn (Koeberlinia), ephedra, many cacti, maguey, 
ocotillo (Fouquieria splendens), and bunch grass. This region has 
been called the sotol country. With gradually diminishing rainfall 
in the Marathon Basin the vegetation becomes more sparse and the 
cylindrical cacti appear, but in the mountains there are junipers, 
_ pifions, and other trees of similar habit. In the Davis Mountains 
small trees, mostly oaks, are also abundant, but in the descent to 
_ Marfa and in the wide basins beyond, the sandy soil has wide-spaced 
_ vegetation, the most conspicuous of which is the abundant yucca 
(Yucca elata). Toward El Paso, more than 900 miles west of the 
