24 



THE AUBIFEBOUS GRAVELS OF THE SIERRA NEVADA 



* 



tremely variable strike and dip. The inclination seems, however, on the whole, 

 to be predominant in a southwest direction, or away from the crest of the 

 range which is much nearer the eastern edge of the mountain mass than it is 

 to the ocean. It would appear that this portion of the Coast Ranges has been 

 lifted up bodily with a general inclination away from the axis of upheaval 

 on its eastern edge, and that numerous minor undulations have been formed 

 at the same time. The deep valleys have been eroded out chiefly by the 

 agency of running water, and the level areas at the bottoms of these canons 

 are usually of very small size. They are sometimes occupied by horizontal 

 or slightly disturbed strata of Pliocene age. Such deposits, however, are 

 rare, and the exposures are narrow and of no great thickness ; they contain 

 an abundance of fossils. Generally, all through the region north of Clear 

 Lake, the Tertiary rocks are extremely subordinate in quantity to the 



Cretaceous. 



The lower part of Trinity and Klamath rivers seems to form the boun- 

 dary between the Coast Ranges proper, and that portion of the Coast Moun- 

 tains which appears to belong, lithologically, to the Sierra. The upper portion 

 of Trinity River runs in a direction parallel to that of the streams flowing 

 down the Sierra slope ; but at Weaverville it turns and flows at right angles 

 to its former course, or in a direction parallel with the ordinary drainage of 

 the Coast Ranges. After running about forty miles towards the northwest 

 it enters the Klamath, which river makes at its junction with the Trinity a 

 similar change in its direction, after having followed a course transverse to 

 the ranges, or towards the southwest, for a distance of a hundred miles or 

 more. The South Fork of the Trinity heads on the north slope of the North 

 Yallo Bailey, and runs, from that point to its junction with the main river, in 

 exactly the same direction as the lower part of the Klamath. All of Trinity, 

 Klamath, and Del Norte counties is an extremely rough region. The main 

 divide of the northern Coast Ranges becomes more and more elevated from 

 Clear Lake north, and the rocks of which it is made up more and more crys- 

 talline, until finally an axial mass of granite makes its appearance, the promi- 

 nent points rising to an altitude of 7,000 or 8,000 feet, To an observer sta- 

 tioned on any one of these elevations, and commanding a wide view over the 

 region, there seems to be no physical break between the Coast Ranges and 

 the Sierra. Scott's, the Salmon, and the Siskyou groups of mountains seem 

 to represent the continuation of the summit elevations of the Sierra proper, 

 and the Trinity Mountains run into these from the south and from the Coast 





