100 IGNEOUS PROTRUSIONS OF MOJAVE VALLEY. 



common to find, here and there water holes, of great depth, and from which, for a few miles down, 

 the river has a body of running water, which ultimately sinks into the sands and disappears, 

 until a new series of water, in holes, is met with lower down. These water holes are true 

 springs, oozing up and overflowing to form the river bed. The temperature of these springs 

 is much more uniform than that of the running water, which, passing over a heated soil, becomes, 

 in a short time^ nearly as warm as the atmosphere ; while the water holes or springs, on the 

 contrary, have a much lower temperature in summer time, and are warmer in winter. These 

 water holes are surrounded by a dense growth of willow, and occasional cotton-woods. 



The difference of temperature observed at camp, fourteen miles below where the trail strikes 

 the river, was — 



') 



-Temperature of the air, in shade 82° F., at 2 p. m. 



Temperature of running water 74° F., do. 



Temperature of water holes 56° F., do. 



At the first crossing of the Mojave, at the foot of the slope from the Cajon pass, is a spring 

 of this character. The water is hard, clear, and of good taste. 



Immediately east of the Mojave, where it is first struck, there extends a low-crested hill 

 running north and south. This hill is not more than three miles from the river, and is 

 approached by a more rapid ascent than that of the left bank. The beds of conglomerate are 

 traceable a short distance up this slope, then terraces of detritus, chiefly of quartz and volcanic 

 rock ; then a compact quartz rock in situ, and the main body of the hill of red amygdaloidal 

 lava and greenstone porphyry. Fragments of these rocks are scattered along the terraces. 



The valley of the Mojave is fertile only on the immediate banks of the river ; there, where 

 the moisture infiltrates through the soil, cotton-woods, willows, grass, and composite flowers 

 grow luxuriantly ; at some distance from the bank, (three or four hundred yards,) the flowers 

 were in clusters, with intervals of bare^ dry, and pulverulent soil, which is chiefly of a sandy 

 character, though occasional clay beds occur. 



On the same day 1[ April 7) on which the foregoing thermometrical readings of the water were 

 taken, the sandy soil was examined for its temperature, six inches below the surface, which, at 

 4 p. m., was found to be 92° F. The hottest part of the day is about 2 p. m., so that the 

 temperature ascertained was that which for five, or perhaps six, hours of the day the soil had 

 attained to. This great warmth of soil starts the vegetation forward early in spring, and from 

 the absence of rain in this region in summer, the plants are burned up by the intense heat of 

 the soil. Perhaps for the same reason they are stunted in height, do not put out branch or leaf, 

 and flower early. The plants not having time to live long enough to increase in size, and then 

 flower, appear to devote all their energies to the propagation of the species. Species similar to 

 those of Los Angeles valley were found in flower on the Mojave ; at Los Angeles some species 

 were eighteen inches and two feet high ; their congeners of the Mojave were two and three inches. 

 From the first crossing, the course of the Mojave, fourteen miles down, is north a few degrees 

 west; then, for more than twenty miles, it is north a little (10°) east; and then, generally, in a 

 true easterly direction, until it terminates in Soda lake. In this course it follows, to a great 

 extent, the dip of the conglomerates, north 10° east. This dip determines the slope and con- 

 figuration of the valley of the Mojave until it disappears ; but here and there the sandstones 

 are broken through, upheaved and contorted by small ranges of hills generally isolated, and 

 running in direction or trend pretty uniformly northwest and southeast. Occasionally a small 



