8 MOUNTAIN RANGES.—TABLE-LANDS.—LLANO ESTACADO. 
sinks into the valley of the Pecos. I do not find an estimate of the general elevation of the 
range, but the summit of the Guadalupe Pass, one of the lowest, was found to be 5,717 feet 
above the sea; while the Hueco Pass is 4,811 feet; and the pass in the Organ mountains, 
between Doiia Ana and San Augustin spring, is 5,467. In fact, the Guadalupe Pass is the 
highest point Captain Pope reached on his whole line. It is important to note here, that the 
Witchita mountains, explored by Captain Marcy and Doctor Shumard, and found to be of granite, 
are located directly in the line of trend of the Guadalupe mountains, and their geological con- 
nexion is thus indicated. The outcrop is, however, very distant; but other knobs of granite 
in a line with, or parallel to, the Witchita mountains, indicate that the general trend of the 
granitic axes or elevations of that region is N. E. and S. W.; and this favors the supposition 
of the prolongation or connexion of the Guadalupe chain with the Witchita. We should thus 
expect to find either more outcrops of granite between the end of the Guadalupe and the Witchita 
mountains, or a very perceptible modification of the surface of the Llano. 
The intervals between the mountain ranges, which are crossed by the line of survey, being 
occupied by high table-lands, the altitude of these ranges above the surrounding surface is not 
great. Captain Pope has described three table-lands, rising one above the other towards the east ; 
their greatest width being at the northeast, and their inclination being very gentle towards the 
southeast; while on the west they terminate in abrupt descents, the three mountain ranges just 
described forming their western limits. Two of these table-lands are west of the Guadalupe 
mountains, and are comparatively narrow; the first, from the Rio Grande to the Hueco mountains, 
being 25 miles; and the second, from the Hueco mountains to the Guadalupe Pass, being about 
80 miles in width. The average elevation of the first, deduced from Captain Pope’s numerous 
observations for altitude, is 3,963 feet, being the mean of 12 determinations at distant points. 
This plain must be remarkably level, and well deserves the title of Mesa, which it receives; for 
the greatest difference in altitude between the 12 stations, from the summit or edge of the 
plain to the Hueco mountains, is only 56 feet; the highest station being 3,991 feet, and the 
lowest 3,935. The second plain is more elevated; and yet its lowest point, at the Ojo del Cuerbo, 
(3,893 feet above the sea,) is lower than any recorded on the first, and is, at its eastern side, 
near the Guadalupe mountains. The slope of the plain, from the summit of the pass eastward, 
appears to be very gradual, and, with one or two exceptions, is remarkably regular. One of 
these exceptions is at the base of the Sierra de los Alamos, which consist of isolated mountains 
rising above the general level of the plain. The mean altitude of this plain on that line, 
according to the measurement of the survey, may be considered as 4,250 feet. 
The western limit of this plain is the range of the Guadalupe mountains, and beyond them, 
to the east, is the broad area of table-lands and semi-deserts, reaching to the Cross Timbers of 
Texas. We here find the great Llano Estacado, or Staked Plain, an elevated treeless waste, 125 
miles in width, on the line of Captain Pope’s survey. The observations for altitude show that 
this plateau is remarkably level, and is unbroken by hills or sudden undulations of the surface. 
The profile shows one great swell of the surface between the Pecos and the Colorado, forming 
two long, but very gentle slopes, similar to the slopes and counter-slopes of mountains and 
continents; that on the east being 130 miles in length, while on the west it is only about 
eighteen miles. The two extremes of this undulation at the beds of the rivers appear to have 
nearly the same elevation—about 4,000 feet; and the highest point between them—the 
‘“‘summit’’ of the Llano, as it is called by Captain Pope—is 4,706 feet. From Captain Pope's 
observations of the general bluff character of all the plateaux towards the west, and the con- 
sideration of the topography of the country further north, I have been disposed to regard this 
shorter or western slope as resulting from the erosion of the river Pecos, and to consider the 
gradual slope eastward from the summit as formerly continuous up to the base of the Guadalupe 
mountains, forming a uniform slope, similar to the two further west, which have been before 
described. It is, however, possible that this great undulation of the Llano, represented in the 
1 The elevation of this Pass is reported by Mr. A. B. Gray to be 4,897 feet. [Railroad Record, No. 136, Oct. 1866, p. 21.) 
