140 GUIDEBOOK OF THE WESTERN UNITED STATES. 
finally, and in the next few miles this rock is seen to extend along 
the base of the mountain to the north and south, underlying the 
younger volcanic series. 
A short distance beyond McConnico is a projecting spur of the 
granite which shows in low cuts on both sides of the track. From 
Hancock, the next station, the railway goes a little west of due south 
across Sacramento Valley, a characteristic southwestern desert con- 
sisting of a long, wide, flat-bottomed valley bordered by mountain 
chains of very irregular outline and sustaining a very scant vegetation. 
The sandy floors of such valleys slope up gradually to the foot of the 
mountains, where they give place abruptly to steep rocky slopes, as 
shown in Plate XXXVII, B. The valleys are underlain by deposits 
of sand, gravel, and other wash from the mountains, and in some 
areas well borings show that deposits of this sort attain a thickness of 
more than 1,000 feet. The detrital materials partly fill valleys that 
were excavated at a time when the region was higher than it is at 
present. ; 
At Drake siding (milepost 527) there are excellent views to the 
west over a typical desert valley to the foot of Black Mesa, 8 miles 
away. This mesa, which rises about 1,500 feet above the valley, 
consists of a great succession of alternating lavas and tuffs similar to 
those at Kingman, in beds tilted slightly to the west. 
At milepost 537 there is a 10-foot cut in the valley filling, showing 
hot summer days and cool off rapidly at night to 70° or less, a differ- 
ence of 50° or more; and in spring or autumn, when the sun heat is 
less, the night temperatures are relatively lower. In winter there is 
frost in the higher lands, but this factor is less effective. 
during showers; and the winter, from December to February, when 
It is too cool for vegetation to advance materially. 
conspicuous plant, covering the desert flats from Kingman, Ariz 
to Hesperia, Cal., is the creosote bush (Covillea tridentata). This 
plant grows 2 to 6 feet high and is rather widely spaced, after the 
habit of desert plants, which require wide-spreading roots in order to 
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