114 GUIDEBOOK OF THE WESTERN UNITED STATES 
Near Torbert siding the valley is very wide, extending north to and 
beyond the Texas & Pacific Railway. It contains much grass and 
many yuccas. Far to the north is a long line of cliffs of limestone 
(Permian) forming the southern margin of the Sierra Diablo.® 
Sierra Blanca is at the junction of the Southern Pacific and Texas & 
Pacific lines (p. 
Sierra Blanca. Texas. 
293) and on State Highway 1, which crosses southwest 
In the vicinity are aaiaeirs cattle ranches, 
and considerable prospecting has been done on the 
Elevation 4,518 feet. 
tion 723. 
Orleans 1,095 results. 
miles 
adjoining mountains, but without very encouraging 
The dominant feature of the landscape is 
the high conical mountain about 8 
miles distant, 
called Sierra Blanca through a perversion of the Mexican name 
“Cerro Blanco” (white hill). 
Its elevation is about 6,970 feet. It 
consists of a huge body of rhyolite, a fine-grained, nearly white rock 
that has welled up as 
crust. 
a viscous mass from a fissure in the earth’s 
The rhyolite lies on a platform of limestone of Washita age, 
which on the west side is penetra 
ted by a large sill of a darker, 
coarser intrusive rock (trachyte), probably older than the rhyolite 
and similar in character to the large lens-shaped intrusive mass that 
ne half a mile south of Eagle Spring, 
southeast of the fault. It is 3 feet 
thick, dips 80° N. 15° E., and has been 
altered to a semianthracite by the heat 
of a great intrusion of igneous rhyolite 
which has also changed some of the 
limestones into marble. A short dis- 
tance up the arroyo, above the old coal 
ee es 
Exogyra quitmanensis and 
texana. Farther up is the tuff Seen 
of the great voleanic mass. A mile 
to the northwest are exposures of shale, 
sandstone, and Orbitulina-bearing lime- 
stone, which crop out at intervals for 
3 — west along the south side of the 
faul 
= the north end of Eagle Mountain 
there are exposures of about 550 feet 
sandy and limy layers, the latter con- 
taining Inoceramus labiatus and other 
fossils of the Eagle Ford formation. 
At. Carpenter Spring, 4 miles south- 
ably on the other limb of a syncline, 
is several hundred feet of shale under- 
lain by limestone, all believed to be 
Finlay. limestone also occurs 
on the northeast side of Eagle Moun- 
tain, where it contains some brown 
sandstone and shale and has yielded, 
according to ans _ fossils Orbi- 
er texanus, Pecten 
8 Just mouth of these cliffs is a long 
west-east fault south of which is ex- 
posed a thick succession of limestones 
and red shales 
siding, one of the most prominent of 
which is Eagle Flat Butte, just north 
of the Texas & Pacific Railway. South- 
ae of Bola siding are ridges of strata 
