SOUTHERN PACIFIC LINES 
165 
range is a large intrusion of quartz monzonite porphyry which uplifts 
limestones of Permian age. 
rocks of Tertiary age. 
There are also some masses of eruptive 
Zinc ore has been produced in considerable 
amount from mines in the altered limestone near the porphyry con- 
tacts. Some of the geologic relations are shown in Figure 41. 
In the © 
ridges north of Columbus a small amount of onyx was quarried at 
one time. 
From Columbus west the railroad Sects across the great plain 
of valley fill and passes around the south end of the Tres Hermanas 
Mountains through 
Mimbres siding. Beyond Mimbres two small 
lava fields are crossed, apparently the product of rather recent 
a ESTE 
Horizontal scale 
gener 59 scale 
o- 
, 5900 Feet 
FiGuRE 41.—Section across Tres Hermanas Mountains, Luna Cou 
¢ 
nty, N. Mex. Cg, Gym limestone 
phyre 
Permian); p, porphyry; r, rhyolite; b, basalt; q, quartzite; k, kerato: 
eruptions. To the southwest are high mountains in the State of 
Chihuahua, Mexico. 
Hermanas is in the entrance to a low gap between the Carrizalillo 
Hills (ca-rree-sa-lee’yo) on the south and the Cedar Grove Moun- 
tains, a ridge 
Hermanas. 
Elevation oe feet. 
Population 
Ni 
the southwest corner of Luna 
beyond Hermanas are the Carrizalillo Springs, a very 
which extends southeastward across 
a8 
unty.2". Two miles 
pit Orleans 4231 good example of underflow water brought to the 
surface by a ledge of hard volcanic rock which here 
crosses the v 
ey 
into the great basin of Lake Guzman, in Mexico. 
To the west is a wide desert valley draining south 
The international 
*t This ridge consists mainly of a 
succession of thin sheets of latite and 
other voleanic rocks of Tertiary age, 
dipping to the northeast at low angles. 
A basal agglomerate crops out along 
the southern foot of the summit. The 
1. 
and also constitutes an outlying | front 
He stati 
rich in soda and carrying little or no 4 
quartz. A ridge parallel to the main 
Cedar Grove Mountains, extending 
He for about 
northwest from 
16 miles, consists of a thick sheet of 
dark lava (basalt) dipping northeast 
and lying on tuffs and other fragmental 
voleanic deposits. also occurs 
at other points in the vicinity of the 
mountains, where it appears to have 
been the Product of the] latest t eruption. 
O11 Walllseaiiitl’ 
ded , Hillis ‘shoe shsetd Of ehipolitd tui and 
relatively short period of geologic time. 
