54 



SCIENCE 



[N. S. Vol. XLI. No. 1045 



succession of shales, sandstones and con- 

 glomerates of Tertiary and Quaternary age. 

 In composition the coast range is in 

 strong contrast with the Sierra Nevada, 

 being much the younger. There are great 

 differences in structure also. The rocks of 

 the coast range are folded, as Lawson points 

 out, in rather sharp synclines and anticlines, 

 some of which are overturned, as in the 

 Monte Diablo region, toward the ocean and 

 thrust faulted, but they are never so closely 

 appressed as to indicate general and impor- 

 tant deformation of the internal structure 

 of the rocks affected. There has been no 

 development of slaty cleavage or schistos- 

 ity. In general, the axes of the folds are 

 northwest-southeast, and although the mi- 

 nor folds may be more or less divergent, 

 the major folds are parallel and extend for 

 many miles. The coincidence of many of 

 the larger valleys with a synclinal axis is 

 very marked. 



The coast range throughout is a faulted 

 range and the faulting has had even more 

 to do with the form of the relief than the 

 folding. Many of the valleys are fault 

 valleys with unsjonmetrical slopes, the fault 

 lying near the steeper slope. The faults, 

 too, are especially interesting because of 

 the earthquakes they produce. Faulting is 

 still in progress, and each slip or movement 

 along the fault plane results in a shock. 

 The great earthquake of 1906 resulted from 

 a slip along the San Andreas rift which 

 has been traced for 600 miles. The move- 

 ment was greatest in the neighborhood of 

 San Francisco and chiefly horizontal in- 

 stead of vertical, as is perhaps generally 

 the ease. Hundreds of faults slip and 

 slight shocks occur in California every 

 year, and perhaps hundreds more too 

 gentle to attract attention. 



The coast range as a whole may well be 

 outlined by faulting. The steep bluff of 

 the coast beneath the shallow and the deep 



sea is probably due to faulting, and the 

 eastern side of the range in Tehama and 

 Shasta Counties has a series of large sand- 

 stone dikes that evidently resulted from 

 an earthquake, possibly in Tertiary time. 

 Unlike the Sierra Nevada, which is mainly 

 one great block tilted so that the streams 

 consequent upon the tilting flow directly 

 transverse to the range, the coast range is 

 composed of many blocks with the main 

 divide along the eastern edge, but the 

 streams, instead of being wholly consequent, 

 taking the shortest route directly to the 

 ocean, are subsequent and follow the lines 

 of easiest erosion along faults and folds to 

 the sea. 



According to Ransome, referring to the 

 work of many others, the structure of the 

 Sierra de Los Angeles appears to show a 

 transition from a combination of folding 

 and faulting such as is characteristic of 

 the coast ranges to tilted block mountains, 

 exemplified by the San Bernardino range, 

 such as are characteristic of the Great 

 Basin. 



Much yet remains to be done before a 

 comprehensive statement can be formulated 

 concerning the structure of the coast ranges 

 as a whole, but with the large corps of 

 workers from the universities at Berkeley 

 and Stanford and the United States Geo- 

 logical Survey as well as others in the field 

 the detailed information is rapidly accumu- 

 lating. 



The coast route from Los Angeles to 

 San Francisco is in the coast range through- 

 out the entire trip and affords an excellent 

 opportunity to observe many of its features. 



THE COAST RANGE OF OREGON 



If in California we have in the Pacific 

 system two ranges, the Sierra Nevada and 

 the coast range, which are strongly con- 

 trasted in composition, structure and age, 

 in Oregon we have two ranges of still 



