52 GEOLOGY. 
from the east; and though dry at the time of our visit, it is evident that its broad and deep 
bed is at times filled with a volume of water which would speedily submerge and convert into 
a lake a large portion of the basin described. 
The altitude of Yampai valley is 3,600 feet, and 1,200 feet higher than the one which lies 
between it and the Colorado on the west. On the south it terminates in the conspicuous 
granitic mass of the Cerbat mountains, to which I have before alluded; and which, with its 
sheets of snow and forests of pines, unites with the green and grassy surface of its southern 
portion to form a beautiful landscape. Towards the north it expands to the width of twenty 
miles, embraced in the diverging ranges of the Cerbat mountains. Its precise length we could 
not determine; but it extends far northward in a nearly level plain covered with grass and 
flowers, and completely encircled by mountains, forming one of the most attractive scenes 
which we looked upon during our journey. The soil is excellent, and with a better supply of 
water it would be as productive as picturesque. 
The caflada, through which we entered Yampai valley at its upper extremity, is cut through 
a thick stratum of trap, which seems to underlie a large part of the plain. Throughout its 
southern half the rocks composing its boundaries are exclusively eruptive in character, but 
the wall which limits its northern portion on the east shows bold perpendicular escarpments of 
stratified rocks. To these, when in the valley, greatly to my regret, I had no access, but after 
leaving it and mounting another step in our ascent, I discovered that these mural faces were 
sections of some of the palwozoic strata of the great table-lands. 
THE EASTERN CHAIN, CERBAT MOUNTAINS. 
The geology of the northern portion of the eastern wall of the Yampai valley is as inter- 
esting and important as that of any other portion of our route; and the inconvenience attending 
an effort to determine the geology of a district. while connected with a party having another 
as a main object, was never more keenly felt than when in the vicinity. We had here the line 
of contact between large areas of which the 
whether their present boundaries had existed 
Did these mountain ranges represent the shores 
re they forced up through the continuous strata of 
If the latter, what has become of the western pro- 
longation of the table-lands; have they been buried in the deep synclinal trough of the Col- 
orado basin? And do we find them represented in the erupted and metamorphic rocks which 
prevail over all the region between this line and the Pacific; or have they been swept away by 
the powerful and incessant action of the waves of the western ocean once rolling so far east- 
ward? 
The key to this great problem is doubtless contained in the vertical faces of sedimentary 
strata before mentioned, but to which we did not gain access. Unfortunately we ascended the 
: 2 , Without having seen its edge, knowing nothing of 
the splendid sections of the table-lands revealed in the cafion of the Colorado, the regret felt 
