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Gueydan Formation
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dan similar to that found in loess. Plate VIII, Figure 1, shows such a valley produced by White Creek in west-central Live Oak County.
The soil of the Gueydan Plain is a light gray to pale buff, rather porous loam or clay-loam. It supports through most of the area a chaparral growth similar to that found in the Gueydan Hills. In that portion northeast of Live Oak County the soil is generally black and rather fertile. Many open, prairie-like stretches occur, but some parts are cov ered with a scattered growth of small oak, mesquite, and other small to medium-sized trees. Along the, major streams north of Duval County are fringes of timbered country.
Mesas. — Interrupting the monotony of the Gueydan Plain in southeastern McMullen and northwestern Duval counties are eight abrupt mesas or groups of mesas rising 100 to 160 feet above the adjacent plain. The largest of these, Loma Alto Mesa, is the highest point in McMullen County. San Caja is the most northerly of the mesas. The mesas owe their existence to the presence of a cap of siliceous-cemented, very hard Oakville sandstone and conglomeratic sandstone. This cap rock, although usually only from two to twenty feet thick, is so much more resistant to erosion than the underlying pulverulent tuff and clay that a surprisingly large amount of the latter has been removed, compared with the volume of the cap rock eroded during an equal period of time. The cap rock is nearly flat-lying, with the exception of San Caja wihere a definite tilt of 5 degrees or more toward the southwest is evident even in a photograph. The flat tops of most of these mesas have given rise to such fanciful names as "Devils Center Table," which is applied to the central mesa of the La Chusa group. A photograph of La Chusa is found in Plate IV of Deussen's paper. The slopes of all these mesas are practically covered with loose slabs of the cap rock left thus by removal of the soft under lying material. Overhanging cliffs are quite common at the base of the sandstone cap.
With the exception of Loma Alto, all of these mesas are situated on the eastern portion of the Gueydan Plain, as is to be expected since they are salients of the Oakville
