1914] Grinnell : Mammals and Birds of tJn Colorado VaUey 57 



the desert within reach, generally not farther than two miles from 

 camp. 



It was. of course, possible to carry a single day's hunt much farther 

 back on to the desert. A distance of from four to seven miles from 

 the river was occasionally reached in day's tramps, for instance, at 

 Riverside Mountain, twenty miles above Picacho, and at Pilot Knob. 



In the nature of the case, our camps were always pitched on the 

 river bank where convenient landings could be made and the boats 

 tied up safely. As is to be expected, the writer now regrets that 

 extended work was not done at certain points scarcely or not at all 

 touched in our 1910 exploration. It would have been a desirable thing 

 to work intensively on directly opposite sides of the river, where it 

 cut through high ground, at three or more points; for example, at 

 The Xeedles. below Cibola, and at the Laguna Dam. 



It must be remembered, however, that we had practically no 

 information to start with, either as to the fauna or local topography 

 along most of the route. We had it all to learn by our own efforts ; 

 and only as experience accumulated could the contrasting sets of facts 

 come into relief, thereby directing our enquiries into more productive 

 channels. 



DESCRIPTION OF THE COLORADO RIVER 



The portion of the .Colorado River explored by the 1910 expedition 

 is altogether below the famed Grand Canon. There is no true 

 "canon" below the Nevada line, the river flowing through its chan- 

 nel in relatively sober fashion. Yuma is very close to 150 miles in 

 a direct line clue south of Needles. While following a general north- 

 to-south course, the many deflections of the river, and especially its 

 meandering through the big valleys, make the distance from Needles 

 to Yuma by the way of the river approximate 285 miles. The altitude 

 of the river at Needles is 460 feet, at Yuma, 125 feet, so that the 

 average fall in this portion of the river is only a little more than 

 one foot per mile. 



Two features of the Colorado River are extraordinary, when com- 

 parison is made with other streams of the North American continent. 

 ( 1 ) The amount of sediment always carried in suspension is very 

 great, so that the flowing waters are quite opaque at all seasons of 



