518 LAVA TERBACES OF THE GILA. Book III. 
oasis in the desert. It is shaded by mezquite-trees, and 
we found it covered with fresh grass just sprung up from 
the seed. Most of the grasses in this region, as also in the 
desert of the Colorado and in many parts of California, 
appear to be annuals : excepting the seed, not a trace 
remains of the growth of the former year ; but this, washed 
by the first summer rains, together with the soil, into the 
hollows around, shoots up in thick masses forming little 
meadows. After a few months, this in its turn dies off, 
leaving the seed to flourish again the next summer. This 
appears to me an important indication as to the possibility 
of cultivating certain portions of these deserts. 
A broad terrace of doleritic lava with perpendicular 
sections towards the valley, extends from hence far down 
the Gila. Our road brought us over a rough tract of 
rocks of the above-named character, where I saw some 
desert plants unknown to me and of very remarkable 
appearance, but I was not able to examine them more 
closely. Reaching the bottom of the valley, we found it 
to be covered with loose sand, either bare and drifted by 
the wind, or covered with an impervious thicket of several 
varieties of ashy-coloured chenopodiaceous shrubs, in which 
thousands of the Californian quail found shelter. A 
variety of these shrubs, called by the Mexicans, Chamisso, 
yields a serviceable food for cattle. Our mules and horses, 
however, would not touch it. The road continued bad 
down the valley. Then through the deep sand which the 
wind had heaped up on the lava terraces, our waggons had 
again to be dragged up to their upper level. The shouts 
and oaths, the cracking of whips, the whining of the mules, 
— the Mexican drivers themselves call it llorar, — the jolt- 
ing of the waggons over the blocks of lava, the black, 
heated masses of rock, looking doubly black in the dark 
