6i 4 POPULAR SCIENCE MONTHLY. 



marked contrast with the steep walled canons. This kind of topog- 

 raphy is to be observed from a point south of Mount Whitney for 

 more than a hundred and fifty miles northward past Mono Lake, and 

 is undoubtedly the remnant of an old base-leveled condition reached 

 during the early Tertiary and preceding the last important uplift. 

 Mount Whitney even has an almost level summit, breaking away 

 into vertical cliffs, which on its eastern side are over three thousand 

 feet high, and form a portion of the cirque at the head of Lone Pine 

 Creek. The plateaulike character is plainly discernible about Mono 

 Lake, where it has been described by Russell. 



At the mouth of each of the canons debouching upon the desert 

 there is a debris cone or fan of remarkable proportions. These 

 fans have been formed by the radial distribution of the debris over 

 the valley bottom below the mouths of the gorges whence the 

 streams issue. The material of which they are formed consists of 

 gravel and bowlders, and has been spread out over many square 

 miles of the valleys. They are among the most striking features of 

 the desert. The long, even slopes, sometimes reaching six to eight 

 miles into the desert, terminate abruptly against the rocky walls of 

 the mountains. To one not familiar with the desert they do not 

 seem of such immense size, but if a climb is attempted this illusion is 

 soon dispelled, for the slope is long and rough, covered with bowlders 

 and intersected with dry water courses. Lone Pine Creek, heading 

 under the great precipices of Mount Whitney, has many of these 

 huge bowlders strewn along its course. By some their position 

 might be attributed to glacial action, but in reality this is not the 

 cause. Six miles below the mouth of the canon there are some ten 

 to twelve feet in diameter, while at various points one to three miles 

 below occur others reaching a diameter of twenty to twenty-five 

 feet. The swiftly flowing streams, at times augmented to torrents 

 by sudden cloud-bursts upon the mountains, are enabled to do an 

 almost incredible amount of work in transporting material. 



At the close of the Miocene began the volcanic disturbances 

 which modified so much of the old topography of the northern por- 

 tion of the Sierra Nevadas. These flows were chiefly andesite with 

 some rhyolite, and issued from fissures along the lines of faulting. 

 The solid flows, breccias, conglomerates, and ash built up great 

 ridges and mountains at many points. Between Lake Tahoe and 

 Mono Lake much of the older surface was buried. From the latter 

 lake southward for seventy-five miles there is a vast barren table- 

 land, while between the North Fork of Owen's River and the San 

 Joaquin the volcanic rocks reach up to and even form the crest of 

 the Sierras for a number of miles. The volcanic eruptions con- 

 tinued through the Pliocene, and at its close occurred another eleva- 



