ANTICLINAL MOUNTAIN RIDGES 1 69 



Besides monoclinal ridges there are other types of mountains in the region 

 traversed which are not so simple in their structure. These are long, narrow- 

 ridges which were formed by an arching of the strata without breaks. (P. 29.) 



In a later publication^ the structural features of this area are 

 again described : 



The monoclinal structure so characteristic of the western portion of the 

 region known as the Great Plain of the Columbia, and of its southern exten- 

 sion in the Great Basin, due to the tilting of fault-blocks, was found to extend 

 to the mountains on the west. As one approaches the Cascade range from 

 the east, the tilted blocks, the upturned edges of which are short mountain 

 ridges, become of larger size, and form the immediate foothills of the main 

 range. This merging of the structure characteristic of the interior basin with 

 the mountains bordering it on the west, so far as my own observations extend, 

 is more pronounced in central Washington than elsewhere. 



A third reference to this region is made in a later report by 

 the same author :^ 



Again, to the east of the portion of the Yakima valley just referred to, as 

 described in a previous report, there are several mountain ridges, such as the 

 two bordering Moxee valley on the north and south — known, respectively, as 

 Selah ridge and Yakima ridge — and Satas ridge, which forms the northern 

 border of the tilted plateau termed Horse Heaven. Each of these ridges is 

 due mainly to the tilting of a block of the earth's crust, capped with basalt, 

 along lines of fracture. This series of faults, and perhaps in part of mono- 

 clinal folds, trends nearly east and west, and some of them cross the Columbia, 

 as, for instance, the break on the north border of Saddle mountain. 



Five ridges of the topographic type mentioned above cross 

 the EUensburg quadrangle, and, by way of comment on the gen- 

 eral statements given above, these ridges may be considered 

 separately, quoting as far as possible any specific mention that 

 may have been made of them in the earlier reports. 



The southernmost of these five ridges is Yakima or Atanum 

 ridge, mentioned in the preceding paragraph. In the earlier report 3 

 this ridge is more accurately described as having "an arched 

 structure throughout" and belonging to the class of "monoclinal 

 folds," but later (p. 52) the possibility of "a break along por- 

 tions of the northern base" is mentioned. The observations 



^Volcanoes of North America, 1897, p. 248. 



" "A Preliminary Paper on the Geology of the Cascade mountains in Northern 

 Washington," Twentieth Annual Rept., U. S. Geol. Surv., Part II, p. 138. 

 3 Bull. No. 108, p. 29. 



