230 GUIDEBOOK OF THE WESTERN UNITED STATES 
age, capped in part by basalt, tilted, faulted, and considerably eroded. 
The name is derived from Indian pictographs on bluffs near the river. 
On approaching Tartron siding the railroad climbs a few feet to 
the nearly level surface of a broad sheet of lava of relatively recent 
age which extends about 17 miles, to a point beyond 
Stanwix siding. This flow, which is wide to the north 
Elevation 729 feet. and south, doubtless came from several vents. The 
New Orleans 1,650 . 
iles. remains of one crater, probably a source of a con- 
siderable part of the lava, is a knob of moderate height 
1miles northwest of Tartronsiding. Alongridg theast of Sentinel 
siding probably marks another outlet. The lava, which is thin near its 
edges, lies on gravel and sand and is of recent origin 
Sentinel. compared with the lavas constituting the summits of 
Elevation 600 feet. the high adjoining ridges that have been uplifted and in 
“nie large part widely removed and cut back by erosion. 
This recent lava undoubtedly dammed the Gila River 
for a while, but the stream has since cut a trench about 100 feet deep 
across its northern portion. In places the younger lava abuts against 
slopes of the older volcanic rocks, and it occupies valleys developed 
since the older rocks were flexed and faulted, a condition indicating a 
long-time interval. Several wells at Sentinel siding pass through 60 to 
100 feet of this lava and obtain agood water supply from the underlying 
sands, which were penetrated to a depth of 1,129 feet. 
From the Sentinel Plain there are extensive vistas across the desert 
to the lofty Growler Mountains, far to the south; to the commanding 
and nearer Aguila Mountain (ah’ghee-la), to the southwest, culmi- 
nating in a high northward-sloping plateau of lava; and to the Aztec 
Hills, to the west. Back to the southeast Hat Mountain (p. 227) is 
conspicuous. To the north are many ranges, mostly of volcanic rocks, 
which lie beyond the Gila Valley. 
In this part of Arizona the railroad crosses wide desert plains, mostly 
covered by creosote bush (Covillea). Very little of this land can be 
reclaimed by irrigation, on account of the scanty water supply. The 
question of water is the most important consideration in these desert 
regions, not only for domestic use and for locomotives, but for the 
cattle industry, which can not exist without it. Tanks created by 
damming draws hold some of the rainfall, but the loss by evaporation 
i feet 
Tartron. 
(tee-nah’has, Spanish for large earthen jars). Wells find water in 
| the gravel and sand of the desert, in crevices in rocks of the mountains, 
a and under some of the lava flows, but the amount is generally small. 
The scant rainfall wets the soil and in large part evaporates, but some 
es underground into the coarser materials, which occur 
