TO RIO SAN PEDRO. 
371 
across the plain, we struck a dry ravine. Following 
this some eight or ten miles, we reached El Sauce^ or 
the Willow Marsh ; which seemed to be the basin 
where the waters collected from the adjoining moun- 
tains and slopes. Here was a great abundance of 
water, which, from the rushes that grew on its margin, 
I suppose to be permanent. Grass was also plenty 
here. Lieut. Whipple by observation found the lati- 
tude to be 32° 05' 09", longitude 109"^ 02' 06'. 
September 3d There was much alarm in camp 
this morning in consequence of the absence of John 
O’Don oghue, one of the computers, who left the track 
yesterday, and did not rejoin us. It had rained heavily 
during the night, with thunder and lightning, giving 
us a pretty thorough drenching, as our tents were in 
a low and unprotected spot. Sent three men and the 
Mexican soldier back to our last camp in search of 
O’Donoghue. The road was now very heavy ; and 
so deep did the wheels sink into the earth, that it was 
with the greatest difficulty the wagons could be got 
along. Many times they became so deeply imbedded 
as to require the aid of several men to relieve them. 
The pack-mules also had to struggle hard to make 
their way over the miry soil. Our perplexities were 
increased by the many small ravines now partially 
filled with water from the late rains, where the wheels 
sunk almost to their hubs, rendering it necessary to 
double the teams ii. order to extricate them. After 
journeying in this manner for six hours, and making 
but twelve miles, we were obliged to stop and en- 
camp without water. We had expected to reach the 
mountains, now but a few miles ofi', and did not take 
