222 
GEOLOGY. 
rivers. In the northern part of the Basin a few streams of considerable length are found, such 
as the Humboldt, Bear Eiver the tributary of the Salt Lake, and Sevier or Nicollet River; but 
when we compare their number and extent with those of the much more limited valley of the 
Sacramento and San Joaquin, on the opposite side of the Sierra, the extreme aridity and want 
of natural irrigation of the region becomes apparent. The principal streams which flow into 
the Basin, in the section which came under our observation, are the Mojave, Johnson’s River, 
and Cotton-wood Creek. There are others of small extent at the entrance to Taheechaypah 
Pass, the Tejon Pass, and one between Cotton-wood Creek and the Mojave. 
The Mojave River is one of the principal streams of the Basin, and rises among the ridges of 
San Bernardino Mountain, whence it flows northward along the western base of the low granite 
range which forms a part of the Pai-Ute range separating the Basin from the Colorado. This river 
has been supposed to be a tributary of the Colorado, hut the survey of Lieutenant Williamson 
has shown that it has no outlet, and that it sinks away in a dry, basin-shaped depression, or 
lake-bed, about one hundred miles from its source. The first point at which we struck this 
-river was about twenty miles northeasterly from the Cajon Pass, where the Spanish trail crosses 
the stream. At this point the river was a broad but very shallow stream, flowing rapidly in a 
bed of sand, without any vestige of rocks or pebbles, except an occasional grain of granite. The 
broad, sandy bed resembles that of the Chowchillas River far down in the plain. The imme¬ 
diate or first banks of the stream are low and sandy, and evidently subject to overflow, as was 
shown by great accumulations of river-sand on their surfaces. This hank, or “ river-bottom,” 
is thickly wooded with cotton-wood and sycamore, (or the plane tree,) and an abundant growth 
of willows. I found the temperature of the water on the 21st of October to be 70°, air, VS 0 
in the shade. 
The phenomena of the complete absorption and final re-appearance of streams are well 
exhibited by this river. It alternately sinks in the sand, and re-appears suddenly as a running 
stream, at points several miles distant; this is repeated several times along its course before its 
final absorption. This stream, and others that flow below the surface of the ground for a part 
of their course, are sometimes observed to increase in volume very suddenly, and in those 
portions of the stream between two points of subterranean current. This peculiarity was noted 
by Mr. Smith, one of the party that journeyed down the Mojave. They crossed the bed of the 
stream and found it perfectly dry, and on returning by the same trail, three days after, water 
was running over a foot in depth. A short distance above the channel was perfectly dry. 
It is very probable that the phenomenon of the re-appearance of these streams above the 
ground, after they have once sunk, is due to the uneven surface of underlying impervious 
rocks, which, in some places, come so near to the suiface that the subterranean water is forced 
above it. A sudden increase in the volume of water flowing in such places, although separated 
from the upper portions of the main stream by several miles of dry sand and gravel at the 
surface, would naturally be the result of a rise in the head-waters of the stream, produced by 
rains or rapid melting of snows in the mountains. 
It was evident from the appearance of the dry portions of the channel of the river, that at 
certain seasons it is much swollen, and that it flows in a continuous, unbroken torrent over the 
portions of its channel that become dry during the summer. 
Johnson’s River rises in the Bernardino Sierra, about half-way between Williamson’s Pass 
and the Cajon, and was named after one of the men who was sent forward to find water. At 
the point where it was crossed by the Expedition, it was about fifteen feet wide and from eight 
