154 W. H. HOBBS REPEATING PATTERNS IN STRUCTURE OF LAND 



In the Bullfrog district of I^evada nearly one hundred faults of steep 

 hade have been recognized which fall mainly within two series, the one 

 nearly north and south, and the other striking north 30° to 50° east, with 

 a number of faults in other directions.^° Matthes'*^ reports from the 

 Yosemite Valley of California that the dominating directions of vertical 

 joints strike north 50 degrees east, north 30 to 40 degrees west, east- west, 

 and north-south; the most prominent series being the northeast-south- 

 west one. In addition to these vertical series, there are two inclined 

 series, one dipping 30 to 40 degrees west and the other about 60 degrees 

 east. 



Figure 28. — Mop of the Tehachapi Valley 



Showing the known faults, formation boundaries, and drainage lines. Full right lines 

 are faults and dotted lines formation boundaries. (After Lawson's map) 



It would appear, also, from statements by Hobson and Hill, that the 

 same directions which control the fracture patterns within the United 

 States have a dominating influence in Mexico. Says Hobson :^^ 



"There are two predominant directions of faults, fractures, and folds in 

 Mexico ; firstly, from northwest to southeast, and, secondly, from northeast to 

 southwest; the latter is less constant than the former. A third less frequent 

 direction is east' and west. . . . The mineral veins, which owe their origin 

 to the volcanic rocks, exhibit very constantly a parallelism to the lines of 

 relief." 



^•^ Ransome, Emmons (W. H.), and Garry: Geology and ore deposits of the Bullfrog 

 district, Nevada. Bulletin 407, U. S. Geological Survey, 1910, pp. 68-69. 



" Personal communication. 



^3 B. Hobson : The volcanoes of Mexico. Scottish Geographical Magazine, vol. 23, 

 1907, pp. 25-27. 



