504 A DESERT OF DUST AND CLAY. Book III. 
We had hitherto been following the course of the river 
of Santa Cruz, which, although its channel was found dry 
in several places, constantly re-appeared. But below 
Tucson it loses itself in the desert, through which our 
road now lay. 
In the evening of July 16th we broke up our camp and 
and entered upon this desert, extending as far as the Gila, 
and in which, according to the latest intelligence, we had 
not to expect to find any water for the distance of eighty 
or ninety miles. 
At the beginning our road led through a thicket of 
mezquite, but gradually all vegetation ceased. Darkness 
had set in, and our waggons toiled through dust ankle- 
deep, the thick clouds of which were, from time to time, 
illumined by the lightning of a thunderstorm over the 
mountains of Tubac and Tumacacori. After several hours' 
toil, we reached a plain covered with hard clay, and 
breathed a purer and cooler air. We continued our 
march in silence through the night. When morning 
dawned, the clayey desert, hard and perfectly barren, 
stretched before us to the foot of the Picacho, a bold 
pyramidal rock, rising abruptly from the plain. I rode 
on in advance of our caravan. On approaching the 
mountain the road began to be moist : here and there 
mud had collected. At length there was the gleam of 
water : a small pool ! a second ! a third ! I jumped off 
my horse, and led it from one to the other until it had 
relieved its thirst ; then I laid down flat on the ground, 
and drank with avidity the yellow clayey fluid. Rain 
had fallen during the night, but insufficient for our 
caravan, which therefore continued its route without 
stopping. 
We halted nearer to the foot of the mountain, by the 
