552 GEORGE DAVIS LOUDERBACK 



THE BOUNDARY OF THE KLAMATH MOUNTAINS 



In the vicinity of the Klamath River (in northwestern California) 

 occurs a large area of crystalline rocks which bear, in many ways, 

 resemblance to those of the Sierra Nevada, and which created con- 

 siderable doubt, when first studied, as to whether this area should 

 be considered part of the Coast Ranges, which topographic conti- 

 nuity would suggest, or part of the Sierra Nevada, to which it 

 appeared geologically related. The Gordian knot was cut by giving 

 it the name Klamath Mountains, and 1 separating it from the Oregon 

 Coast Range on the north, the Cascade Range on the northeast, the 

 Sierra Nevada on the southeast, and the California Coast Ranges on 

 the south and southwest. As this region has a geological individuality, 

 and as the multiplicity and vagueness of local names for its parts 

 tended to considerable confusion, it was a decided step in advance 

 to characterize this province, delimit it, and give it a comprehensive 

 name. For following up this idea and working out the details we 

 are chiefly indebted to Mr. Diller. 



The present investigation has shown that in southwestern Oregon, 

 down to about the Rogue River, the geological formation, structures, 

 and other conditions are such as prevail in the California Coast 

 Ranges. The Franciscan series is particularly well developed to 

 the southwest and south of the Klamath Mountains in Humboldt, 

 Mendocino, and Lake Counties (lat. 4i°-39° N.), and beyond, in 

 all respects like the Franciscan (Dillard) to the north of the Klamath 

 Mountains in Oregon. It would seem most consistent, therefore, 

 and satisfactory, to omit the Franciscan and Shasta areas on the 

 north from the territory to be included under the title of Klamath 

 Mountains. This would remove the northwest and the northeast 

 lobes as represented on the various maps of the Klamath Mountains, 2 

 and make the boundary cut across toward the west from near Jack- 

 sonville and follow close to the Rogue River until a short distance 

 below the mouth of the Illinois, then west to the coast. In other 

 words, the Klamath Mountains would be that general uplifted region 

 characterized by a nucleus of metamorphic (and associated igneous) 



1 See Powell, Physiographic Regions of the United States (1895), p. 96 (Mono- 

 graph, National Geographical Society). 



2 E. g., that published in Bulletin iq6 (Plate I) of the U. S. Geological Survey. 



