294 W. LINDGREN — TWO NEOCENE RIVERS OF CALIFORNIA. 



pay for drifting is a very doubtful question. It is accessible only by 

 Long and costly tunnels from the North fork side or by inclines from the 

 rims. There are but very few quartz mines along the upper course; the 



channel here enters the generally barren granitic area of the high Sierra. 



Near Soda Springs the deep canyon of the North fork has cut through 

 the channel, exposing on both sides the deep volcanic flows and the curve 

 of the old valley. Section L L is laid across the valley a little south of 

 this and shows sufficiently clearly the relations at this point. At Soda 

 Springs the recent river is about 200 feet below the Neocene channel. 



We are now near the headwaters of the ancient river; on all sides rise 

 bed-rock ridges and peaks, prominent in Neocene as well as in the pres- 

 ent time. North of the North fork the old channel begins to rise rapidly 

 toward the summits. The valley opened up in a sort of amphitheater; 

 one branch extended up toward mount Lincoln, another toward Soda 

 Springs station. The principal valley extended up toward a point about 

 a mile west of Summit station, and its continuation can indeed be traced 

 a little further northward toward the high granitic counterforts of Castle 

 peak. The Neocene river, broad and magnificent on the Forest hill 

 divide, is here nothing more than a ravine. 



Grades : 

 Russian ravine to French meadows, 6 miles, 100 feet to the mile. 

 French meadows to Soda Springs, 10 miles, 115 feet to the mile. 

 Soda Springs to Summit, '3 miles, 200 feet to the mile. 



Discussion of Grades. 



On plate 6 a first, and in many respects incomplete, attempt has been 

 made to show in a comprehensive manner the more important facts 

 about the present grade and directions of the ante-volcanic Neocene river 

 beds. 



Before endeavoring to draw any conclusions from the present condi- 

 tion of these river beds it should be pointed out that the Sierra Nevada 

 is a very heterogeneous mass, composed of rocks of very diverse texture 

 and hardness, which are apt to influence the grade of the rivers flowing 

 over them. Sudden changes of grade are indeed not uncommon in the 

 present rivers as well as in the Neocene channels. It follows from this 

 that conclusions drawn from short distances of channel or based on 

 isolated occurrences cannot he reliable. 



An influence of direction on grade probably also exists, inasmuch as 

 streams flowing parallel to the direction of the range would lie expected 

 to have a slighter grade than those breaking across the strike of the slates 



