4 GEOLOGICAL REPORT—THIRTY-FIFTH PARALLEL. 
gentle slope eastwardly. The Aquarius mountains are different in their topography, and are 
irregular and broken in outline. Their average elevation is probably near 6,000 feet. The 
trend or direction of the ridges is well marked ; the Aztec range trends north 38° west, while 
the direction of the Aquarius range is more northerly, and thus the two ranges unite a short 
distance north of Cactus Pass. 
Cerbat Range.—The Aquarius range is separated from the Cerbat by the valley of Bill Wil- 
liams' fork, which flows southerly for a long distance between these two ranges. This valley 
was followed by the survey until it turned the southern point of the Cerbat range, and thus this 
elevation does not appear on the profile. "The same valley was followed to its junction with the 
Colorado river, and there the valley of this stream was followed northward to a point nearly 
west of the Cactus Pass, or from the place where the valley of Dill Williams' fork was entered. 
The survey, in thus deflecting to the south, turned the southern end of a wide region which is 
traversed by mountain ranges. The breadth of this region measured southwest from Cactus 
Pass to the point where the Colorado was crossed, is about fifty-five miles. It is essential, in order 
to understand the connexion of the leading features of relief of the region with its geology, that 
the ranges or combination of ridges which traverse that space should be represented in their 
relations to the others. Ifthe profile accompanying Lieutenant Whipple's report were intended 
to represent the relief of the region, the space which now exhibits a broad valley or depression 
occupied by Bill Williams' fork and the Colorado, should be filled by the outlines of one or 
more ranges equal in elevation and magnitude to those on either side. As we are without a 
profile of these ranges, determined by instrumental observations, their outlines and elevations 
can be only approximately given ; but as the space which they occupy was seen from both sides, 
and the line of survey passed along and around their southern ends, the profile presented 
with this report and the estimates of altitude may be received with confidence. 
According to Lieutenant Whipple, and Mr. Campbell, the civil engineer who accompanied 
him, the elevation of the Cerbat range is about 5,000 feet above the valley of Bill Williams’ 
fork, and thus 6,500 feet above the sea. Its direction or trend is nearly north 40° west, or 
nearly northwest and southeast. It is probably composed of many ridges, with their trends 
oblique to the direction of the whole series, and they appear to abut upon and to cross the river 
at intervals, thus connecting with the Aquarius range on the other side. Their extent northwards 
is not known, but the chain probably does not retain its full altitude towards the Colorado river. 
It may, however, find a prolongation beyond this stream, and connect with the ridges which 
bound the Great Basin on the east. The great range of the Humboldt mountains is found on 
the lines of prolongation of the Cerbat and other adjoining ranges, if they are curved more 
towards the north so as to conform to the trend of the ranges in the southern part of the Basin. 
Ranges along the Colorado.—Beyond the Cerbat range, to the west, a broad plain or slope was 
seen. This, in some directions, appeared to extend to the base of the ranges along the Colorado. 
Captain Sitgreaves, however, who crossed this space between the rivers a short distance further 
north, represents an intermediate range parallel with the others. I have, therefore, indicated 
one on the map and section. The ranges along the Colorado appear to be much broken, and 
some of the ridges trend obliquely across the river towards the northwest. At the point where 
the Colorado was crossed, a high range was visible in the north along the left bank of the 
stream, and the mountains on that side, at the crossing, appeared to be but the southern prolon- 
gation of this range. Captain Sitgreaves, who crossed this range further north, found it to con- 
sist of rugged ridges, and the highest part of his trail was elevated about 3,200 feet above the 
river. A short distance below the place of crossing, one of the ridges impinges on the river 
and appears to extend across it, shutting off the river towards the south, and thus forming the 
southern boundary of the alluvial valley or bottom-land of the Mojaves. Another range 
extends along the western or right bank of the stream, its southern termination be- 
ing just north of the trail. This range forms a portion of the system which separates the 
Colorado from the Great Basin. The valley of the Mojaves, or Ah-mok-dves, as they are more 
