EXTENT OF THE DESEET-NATIVE COPPEE. 
133 
most layer is a mass of blackish, basaltic rock, ten feet thick, and almost horizontal; lower 
down it merges into a dark green augitic amygdaloidal rock, the cavities being filled with 
white earthy matter which drops out on weathering of the rock, the latter appearing to he a 
vesicular lava. 
Standing on the granitic mesa at the foot of these mountains, and looking backwards over 
the trail travelled, the character of the country becomes apparent; it is an immense extended 
plain as far as the eye can reach, (about sixty miles,) sloping slightly to the southwest, and 
equally level north for thirty-five miles, the horizontality only disturbed by the isolated hills 
or ranges described, whose general direction is north 60° west. The soil of the plain is uni¬ 
form, a felspathic or granitic sand, with occasional drifts of fine quartz sand, easily impressed by 
the hoof of the beast, and brilliant, so as to pain the eye in midday by the reflection of the sun¬ 
light. There is not a particle of humus or mould in the soil, nor is there any opportunity 
for its production ; as there is no running river or stagnant water on this mesa land, none but 
the most desert or thorny plants can sustain themselves in such situations ; no tree or herba¬ 
ceous shrub is found after leaving the valley bottom ; and from this point to the Gulf of Cali¬ 
fornia, on the elevated land, it is a continuous desert, whose character is aggravated the nearer 
the level approaches that of the gulf. 
Between Big Horn mountains and the basalt mesa the bed of the Gila spreads out into a flat, 
which in places is swampy and overgrown with willow, but generally has a fertile alluvial clay 
soil, slightly calcareous, producing abundance of grass ; it averages three to four miles wide, 
bounded by a small terrace thirty feet high, composed of fine sand and clay, and covered over 
with jasper pebbles. 
The alluvial soil contains numerous angular quartz fragments. 
About five miles north of camp, (June 22,) at the base of Big Horn mountains, are two small 
hills, one flat-topped and more easterly conical; on the western edge of the latter, or in the 
trough between the two hills, which are not more than 600 feet high, is a vein of native copper, 
which is found distributed a mile distance from the hill along the bed of a rivulet. The party 
who brought in the specimens (on foot) described the ore as found very abundantly. Accom¬ 
panied by a single private soldier as escort, I crossed the river to examine the locality of this 
native copper, samples of which had been brought into camp the day previous by that individual. 
After a delay of some hours in finding a fordable spot in the river, (as it abounds in quicksands 
here, and forms a series of islands,) and in endeavoring to force a passage through the brush¬ 
wood lining the bank, we at length arrived at the place near where the copper had been picked 
up. It was in an arroyo (dry bed of a small stream) which descended from the most westerly 
of the two hills, and small specimens of the ore were found in the creek bed, accompanied with 
metamorphic sandstone and basalt. The ore was no doubt in the hill higher up; but as the 
camp had moved on, and we were some hours behind, it was not deemed safe to remain any 
longer in the locality, and we retraced our steps to meet the trail. 
These small hills belong to the Big Horn range, and there is little doubt that those also con¬ 
tain this metal at points where trappean intrusions occur. They are described by travellers as 
yielding it fifty miles further south along the range. It is a very rich ore of copper, yielding 
above 80 per cent, of pure metal; the seam is narrow, not more than two inches wide. There 
is much facility for obtaining and transporting the ore at this point. The hills lie within a 
couple of miles of the river, whence by rafts or flat-boats the ore could be carried to Fort Yuma, 
and tbence by steamer to the Gulf of California. The smelting of this ore by a blast furnace 
