HYDROGRAPHIC REPORT. ll 
mediately above is a lone rock, fifty feet from the left bank, the top visible a little way above 
the surface. A difficult shoal occurs beyond. A few miles further the centre of the river is 
again occupied. A rock shaped like a light-house stands midway between the banks. The 
channel on the east side is the proper one to be followed. It is but thirty feet wide, but 
presents no obstructions. Some sharp turns around rocky corners make the next pass a little 
hazardous, and then, through a narrow porphyry gate, the Great Colorado valley is entered. 
The head of this valley is one hundred and ten miles from Porphyry Gate, and the navigation 
throughout its whole extent is similar to that below Fort Yuma. The current has the same 
velocity. The average depth of the channel is seven or eight feet. The best water is usually 
found close to the concave banks. In several places flats are encountered similar to those 
above Fort Yuma. They are generally filled with snags; the water divided into numerous 
channels, and the navigation troublesome. In the vicinity of the Half-way and Riverside 
mountains the river is better than in any other portion of the valley, excepting at one place, 
the Sand island shoals, where two channels are formed by an island, and these subdivided, 
occasioning a succession of difficult bars that require much time and labor to pass. There are 
few places in this valley where the condition of the river is at all permanent, and it is there- 
fore impossible to describe in detail the different localities. 
Beaver island is at the commencement of the foot hills of the Monument mountains—a range 
intervening between the head of the valley and the mouth of Bill Williams’s Fork, twenty 
miles above. At the foot of the island is a little cove, which affords a good place for a steam- 
boat to lay by. In the cafion formed by the foot hills and mountains the river is narrow and 
the water generally deep. The navigation could be pronounced better than at any place 
above the mouth were it not for the occasional appearance of sharp, jagged rocks, projecting a 
foot or two above the surface, and indicating danger when the water is two or three feet 
higher. Four miles from the mouth of the fork there is a sunken rock near the right bank. 
All of the rocks observed were quite close to the shore. During the high stage of the river, 
unless the current should be very swift through the confined passage, the navigation of this 
cafion would be attended with no trouble. 
Throughout the section just described the character of the Colorado differs little from the 
portion below Fort Yuma. Though isolated rocks are met with, the bed is composed of sand, 
and the bars have about the same depth upon them. The obstructions are, however, much 
more numerous than they are below the fort, and the navigation attended with more delay. 
BILL WILLIAMS’S FORK TO PYRAMID CANON. 
This section, one hundred miles in extent, comprises the Chemehuevis and Mojave valleys 
and the cafion through the range which separates them. The navigation in this caiion is 
somewhat like, though much better, than in the cafion through the Monument mountains. 
The river is narrow and deep, and free from bars. There are neither sunken rocks nor any 
that are visible above the surface. There are indications that during the freshet the water 
rises to a prodigious height in some of the narrowest portions, and at that time the ascent or 
descent should not be made without great caution. At other seasons no obstacle will be 
encountered. ; 
In the lower part of the Chemehuevis valley are many shoals, where the bottom is composed 
of coarse gravel, and it is hard to force a boat over the unyielding surface. A slight difference 
in draught would be a matter of great importance in this part of the river. The least depth 
found was twenty-two inches. Upon all of these bars there is a swift current, which enhances 
the difficulty of crossing. Through much of the valley the river flows between gravel bluffs, 
one or two hundred feet high, and here the navigation is good. Where the banks are bold 
