48 GEOLOGICAL REPORT—THIRTY-FIFTH PARALLEL. 
granite, and the general configuration of that region, may be understood by the section given 
with the translation of Mr. Marcou's notes. "T 
''he cliff of limestone which is mentioned between Camps 100 and 102 is probably a continu- 
ation of the bed which outcrops on the western face of the mountain. The granite which under- 
lies these stratified rocks was reached in Aztec Pass, just beyond Camp 102. A specimen of this 
rock from Pueblo creek is an amorphous compact mass, of a reddish color, probably feldspathic. 
It is marked metamorphic by Mr. Marcou, but its mineral characters are not distinct. Speci- 
mens of specular iron ore were also found in this creek, and are described in Chapter X. The 
outcrop of granite appears to be prolonged towards the southeast, where a range of mountains 
was seen, which are probably the prolongation of the Aztec range, and which in all probability 
have a similar geological structure. 
After crossing the range at the Aztec Pass, the trail turned north, following the base of the 
cliff, and at Camp 105 rising upon the bed of sandstone which underlies the carboniferous lime- 
stone. Camp 106 was upon the limestone, but, for a short distance between the two camps, the 
road led over a field of lava. The underlying granite was found beyond Camp 106, and, with 
a few exceptions, where covered by lava and modern deposites, was the only rock seen as far west 
as the Aquarius mountains. The nearly horizontal carboniferous strata of the Aztec mountains 
were found to be continuous north of the trail, and formed the top of Cross mountain, which 
terminates just north of Camp 109. 
Cygnus Mountain.—About ten miles south of the part of the route just described we find a 
range of high peaks about twelve miles long, and which are probably volcanic. This elevation 
has been called Cygnus mountain by Captain Whipple, and is probably the source of the lava 
streams which are crossed at various points between Camps 105 and 110. The lava probably 
covers the greater part of the surface lying between the Aztec and Aquarius mountains. Mr. 
Marcou calls this elevation Whipple mountain. He considers it volcanic, but intermixed with 
granite. | 
Aquarius Mountains.—This range, of which a physical description has already been given in 
the first part of this report, consists chiefly of granitic and metamorphic rocks. It has a gen- 
eral parallelism with the Aztec mountains, but is without the overlying carboniferous strata, 
which impart so much interest to that range. The survey crosses the northern portion of this 
range along the valley of White Cliff creek, to which the name Cactus Pass has been given. 
On the eastern side of the pass Mr. Marcou found outcrops of gneiss, overlaid by sandstone 
and conglomerate, which dipped to the east. The conglomerate appears to be a mixture of 
volcanic ash and angular fragments of lava. It was thought to be Tertiary by Mr. Marcou. 
Granite was found beyond, and then beds of sandstone and limestone, also considered Tertiary, 
were found. These strata were upheaved, and dykes of trap and red porphyry traversing 
them were found. The trend of these outcrops was north and south. At the summit of the 
pass Mr. Marcou found a large vein of red sienite trending north and south; afterwards gneiss 
and quartziferous porphyry, traversed by veins of white quartz. The gneiss is contorted and 
dips to the west. Granite was again found as far as Camp 112, in the valley of Bill Williams’ 
fork, at the base of the western slope. The granitic rocks of the Aquarius mountains are well 
represented in the collection, (See the catalogue and descriptions, Nos. 9, 10, 11, 12, 13, 16, 29, 
and 50.) No. llis a specimen of the rock from the summit of the pass ; it is composed of coarse 
crystalline fragments of brilliant red feldspar and white translucent quartz, with a little dark 
mica. No. 9, from the eastern side of Cactus Pass, is a compact rose-colored granite. The line 
of survey in following down the valley of Bill Williams’ fork, called Big Sandy creek by Mr. 
Marcou, passed along the western base of the Aquarius mountains for fifty miles. But the 
range was not crossed again, and few or no additional specimens were collected. 
Valley of the Hawilhamook or Bill Williams’ fork.—In descending the valley of Bill Williams’ 
fork, Mr. Marcou noted drift deposites on each side of the trail, which appeared to extend 
west as far as the foot of the Cerbat mountains on the opposite side of the river. This drift 
