GRANITE—SLOPE OF THE GREAT BASIN-VEGETATION. 
63 
we reached Johnson’s river, a powerful and rapidly flowing mountain stream, a few yards wide. 
The water was very pure and cold. The channel or bed of the river was filled with rounded 
blocks of granite, syenite, and metamorphic rocks, probably all derived from the ridges among 
which the stream flows. No basaltic or trappean rock was seen. Some of the syenites were, 
however, very compact and fine-grained. We encamped on the eastern side of the stream ; 
nearly opposite us, there were outcrops of granite, light colored, and decomposing rapidly. It 
was found to he traversed by great veins of quartz and feldspar. Mr. Ridley, who had 
travelled among the lower ridges between our last camp and this river, brought me several 
specimens of agate and carnelian which he had picked up. 
Johnson’s river to the Mojave , October 18.—A trial was made of the sand along the margin of 
the stream for gold. Several pans-full were washed out without finding the color. Black sand 
and garnets were very abundant. The sand and gravel were, however, not taken from the bed¬ 
rock ; this could not he reached in the short time before starting from camp in the morning. 
No slate rocks, such as usually bear gold, were seen. Mr. Smith obtained a large peice of white 
limestone from the top of the hill on the right of camp. This hill and others in the vicinity 
appeared to be formed of sedimentary rocks in horizontal strata, probably Tertiary. 
The route of the Expedition from this river was in a direction a little south of east, over, the 
broad slope of the Great Basin, being below the foot-hills of the mountains, and yet only a few 
miles distant from them. The slope was broad and gentle, extending for nearly fifteen miles 
from the mountains without its surface being broken by a ridge or diversified by trees of any 
magnitude. When looking in advance, the inclination was very evident, and opposite the Cajon 
Pass there seemed to be a swell of the ground, so that the outline of the descent was brought 
very distinctly into view ; its inclination was approximately obtained by the clinometer, and the 
angle was found to be between five and seven degrees. Near the mountains the surface was 
uneven, and furrowed by the channels of streams, then entirely dry ; but lower down, all these 
channels were obliterated, or became so shallow as not to offer any impediment to the passage 
of the wagons. In the banks of these 'dry streams the nature of the materials composing the 
slope was fully exposed, and generally appeared unconsolidated and rudely stratified, in many 
places much resembling ordinary till or drift. 
The higher parts of the slope are covered with a thin growth of the yucca, or Spanish bayonet 
tree, occupying a belt three or four miles in width. They are interspersed with cedars, which 
grow to be large shrubs or bushes, and do not form high branching trees. The trunks are, 
however, quite large—some being over a foot in diameter, and the limbs spread over a wide 
surface, but the height rarely exceeds twelve or fifteen feet. Sage bushes, ( Artemisias ,) and many 
small thorny shrubs, grew thickly together in many places between the cedars. Bunch-grass was 
also common, but was entirely brown and dry. 
About sunset a small running stream was unexpectedly found. It was not bordered by high 
banks, nor were there any trees on its borders. It seemed to be a temporary flow from the 
mountains. After resting at this point until late in the evening, the journey was resumed by 
moonlight. The air was slightly charged with moisture, and at first the stars were but dimly 
seen. The course lay, as before, over the unbroken slope parallel with the mountains. The 
party in advance lighted up their trail at intervals, by piling dry shrubs and bunch-grass 
against the windward sides of the cedar bushes and igniting them. They produced broad sheets 
of flame, and made excellent beacon fires. As the day began to dawn in the east, and the out¬ 
lines of the mountains beyond the Mojave river became visible, we reached the old Spanish trail, 
