50 



SCIENCE 



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



the east and the coast ranges, including the 

 Klamath mountains of California and Ore- 

 gon and the Olympic mountains of Wash- 

 ington on the west from near the Mexican 

 line to British Columbia. They are sepa- 

 rated by a depression, a great valley more 

 or less continuous from the Gulf of Cali- 

 fornia and Salton Sea on the south through 

 the Great Valley of California, the Wil- 

 lamette Valley of Oregon and Puget Sound 

 to Georgian strait on the north, which it 

 enters and follows with less definition 

 along the coast of British Columbia to 

 Alaska, a total distance of about 2,500 

 miles. 



In the United States there are only three 

 rivers, the Columbia, the Klamath and the 

 Sacramento (including the Pit), which cut 

 across the entire mountain belt from the 

 interior platform to the sea, although three 

 others, the Chehalis, Umpqua and Eogue 

 rivers, rise on the west slope of the Cascade 

 range and break through the coast range. 



The mountain ranges which now consti- 

 tute the topographic limits of the Great 

 Valley of the Pacific coast are composed 

 of parts that differ widely in origin, age 

 and composition. 



THE SIERRA NEVADA 



The Sierra Nevada is a massive mountain 

 block, 350 miles long and 80 miles wide, 

 with a long gentle slope west to the Great 

 Valley, and to the east has a short steep 

 slope, due to faulting, that separates the 

 rocks of the Sierra from those of the Great 

 Basin. 



The Sierra Nevada is composed of sedi- 

 mentary and igneous rocks of various ages, 

 from Silurian to Jurassic, which have been 

 closely folded and intruded by batholithic 

 masses of granitic rocks. The folding and 

 intrusion have greatly altered the rocks 

 and developed in them numerous metal- 

 liferous veins, chiefly of auriferous quartz. 



During a long period of erosion which 

 washed away the mountains and reduced 

 the country to low relief the veins gave rise 

 to auriferous gravels, and some of the 

 earlier of these gravels in the northern por- 

 tion of the range are covered by flows of 

 Tertiary lavas. 



The southern and central portion of the 

 range where granodiorite prevails is one 

 great topographic block bounded on the 

 east by a fault zone, which curving to the 

 west around the southern end, meets the 

 San Andreas fault of recent earthquake 

 fame and brings the Sierra Nevada and the 

 Coast range together. In the northern por- 

 tion of the range along the eastern side of 

 the great block, adjoining the Great Basin 

 and suggesting its structure, there are two 

 smaller fault blocks, one of which locally 

 has sunk for Lake Tahoe, while the other 

 forms the bold eastern escarpment of the 

 range. 



The Tertiary lavas of the Sierra Nevada 

 are continuous to the northward with the 

 great pile of volcanics in the Cascade range, 

 beneath which the older terranes of the 

 Sierra Nevada disappear with a strike of 

 approximately N. 50° W. toward the Kla- 

 math mountains, about 60 miles away. 

 Some minor faults appear in the lavas of 

 the Lassen Peak region but major faults 

 like those which characterize the Sierra 

 Nevada have not yet been recognized in 

 the Cascade range. 



The faulting which limits the Sierra 

 Nevada on the east, as emphasized recently 

 by Ransome, has been of long duration and 

 is still in progress, as evidenced by the 

 many small earthquakes at points along its 

 course. The Owens Valley earthquake of 

 1872 is the most notable example resulting 

 from a fault of 10 feet. 



The earthquake was widely felt, but 

 there are many that are not felt at all under 



