GEOLOGY OF THE COAST RANGES. 



23 



Mount Harbin, and Uncle Sam arc all volcanic. To the cast of Clear Lake 

 there are to be observed many most interesting phenomena of active volcan- 

 ism ; hot springs, small lakes holding boracic acid in solution, sulphur banks, 

 and other occurrences of similar origin are well displayed over an extensive 

 area of country. So far as our knowledge goes, there is an entire cessation 

 of these volcanic phenomena in the region of the Coast Ranges to the north 



of Clear Lake. 



Deposits of gravel of any importance are not usually to be found in the 

 portion of the mountains which has just been noticed; but there is one, 

 which is quite extensive, in the neighborhood of the north fork of Cache 

 Creek, about twelve miles east of Clear Lake. This deposit first shows itself 

 at Chalk Mountain, and it extends off to the south, widening in that direc- 

 tion, for a distance of ten miles, and occupying a triangular area between 

 Lower Lake, Chalk Mountain, and the head of Grizzly Gulch. It is every- 

 where stratified, in usually nearly horizontal layers, and is made up of mod- 

 erate-sized boulders of the metamorphic rocks occurring in the region, mixed 

 with water-worn fragments of unaltered shales and sandstones. This remark- 

 able deposit has a thickness in places of as much as 400 feet. No fossils have 

 been found in this gravel ; but it seems to resemble the Pliocene strata 

 already noticed as occurring in the vicinity of San Fernando Pass, and in 

 other places farther north. It has been deposited prior to the cessation of 

 "volcanic action in this region, for a stream of lava coming down from High 

 Valley, a little east of the centre of Clear Lake, has flowed over it in one 

 place. 



North of the parallel of 39°, as for as the Klamath River, there is much 

 Monotony in the geological structure of the Coast Ranges. The rocks are 

 almost exclusively Cretaceous, and often very much metamorphosed, jaspers, 

 serpentines, and even mica-slates, occurring in large quantities, and in the 

 ttiost irregular manner ; but there are also many areas of quite unaltered 

 strata. The topographical features of the country are on a large scale, the 

 valleys being deep and precipitous, the ridges lofty and extensive. The 

 Sundance of chaparral, and the depth of the soil over a large portion of the 

 Northern Coast Ranges, makes their exploration exceedingly tedious and 

 ^satisfactory, and the dilliculties of making out the structure are greatly 

 ln creased by the crumbly character of the unaltered strata, and the extreme 

 irregularity of the metamorphic areas. It is a constant repetition of jaspery 

 belts, imperfect serpentines, and coarse non-coherent sandstones, with ex- 



