DRAINAGE FORMS 299 



to the slate and limestone country, as a large mass of quartzite often 

 stands out very ruggedly, its brown color and coarse angular talus fre- 

 quentl}' giving it the appearance in the distance of a massive lava. 



The drainage lines are gullies and canyons which are commonly steep- 

 sided and often very narrow and gorgelike just before their debouch- 

 ment on the valley's edge. Higher up they may open out considerably 

 , into a blunt V-shape. There is a distinct tendency for the stream lines 

 to become subsequent, but that character has been only partially devel- 

 oped. It is most noticeable in the intermediate and also the upper 

 courses of the lower parts of the range, where the lateral branches fre- 

 quently lie in strike gullies for comparatively long distances. The lower 

 courses of all stream lines and the entire courses in the higher and steeper 

 parts of the range are decidedly independent of the structure, lying nearly 

 perpendicular to the present range front, whatever be the attitude of the 

 rocks, and branching back like fingers from the main trunk. The mouth 

 of Muttleberry canyon is somewhat exceptional in this regard, for as it 

 comes down in the direction of the dip, though with a grade consider- 

 ably less than the dip angle, it makes a sharp turn to the south for a 

 couple of hundred yards and debouches on the valley along the strike. 



Another form of stream topography is the fault-line gully or canyon. 

 By this is meant any drainage line the two slopes of which are in faulted 

 relationship with each other, the trace of the fault-plane approximately 

 coinciding with the stream trace. The fault may have no other physi- 

 ographic expression and is then determined solely by the lack of har- 

 mony of the strata of the two sides of the canyon. A half dozen of such 

 occurrences were observed within a five- mile belt on the west slope of 

 the mountains, two of which have already been described and illustrated 

 under faults.* 



Relation to range outline. — While the foregoing phenomena are of 

 value with respect to the main problem before us, by far the most impor- 

 tant geomorphic consideration is the relation of the form and topogra- 

 phy of the range as a whole to the structure and attitude of the bedrock 

 series. 



The southern division of the Humboldt mountains forms a continuous 

 range about 42 miles long. It rises out of a flat valley on either side, 

 and, if we imagine the alluvial cones removed, its slope presents a prac- 

 tically continuous flowing curve as a trace upon the valley plane f — that 

 is, there are no mountain lobes passing out into the valley, no bays or 

 low, flat subordinate valleys passing into the range from the main val- 



*See the longitudinal faults on detailed section, plate 21, and also the transverse fault described 

 on page -297. 



fThe Lake Lahontan shorelines affect this appearance, in some degree, on the gentle slopes of 

 the low parts of the range, but are everywhere quite easily eliminated from consideration. 



