A NTICLINA L MO UNTA IN RID GES I 7 3 



respect is Umptanum ridge of the nature of a faulted mono- 

 clinal fold. 



Manastash ridge likewise exhibits the anticlinal structure, 

 unsymmetrical, and again with the steeper dips on the north limb. 

 In the vicinity of Yakima river there is a fault present, as shown 

 in the area! distribution of the formations. This fault, however, 

 produces no scarp, and indeed crosses slightly the topographic 

 axis of the ridge, showing the impossibility of its having an}- part 

 in the elevation of the ridge. In fact, this fault belongs to a 

 period of deformation antedating the uplift of these ridges to 

 their present elevations. Throughout the region the orographic 

 history has been more complex than is indicated in this article, 

 where only those facts are cited which bear upon the points in 

 question. 



Farther east the Manastash ridge uplift unites with others to 

 form Saddle mountain, which is cut through by Columbia river 

 at Sentinel bluffs. The structure of Saddle mountain was des- 

 cribed by Professor Russell as follows :^ 



Saddle mountain, as previously mentioned, belongs to the series of mono- 

 clinal uplifts due to faulting, which extend eastward from the foothills of 

 the Cascades. This long, narrow, sharp-crested ridge is perhaps the most 

 remarkable of these uplifts, as it extends farther east than any of its compan- 

 ions and clearly reveals its structure where the Columbia has cut through it. 



It is there a well-defined monoclinal ridge, dipping sharply southward 

 and presenting a bold scarp to the north. The dip of the strata of basalt of 

 which it is composed corresponds with the gently sloping southern side. The 

 line of fracture is on the north side of the ridge, and the steep northern face 

 is a fault scarp. Toward the eastern end the fault scarp decreases in height 

 and finally dies out, and the John Day beds pass over and conceal the Colum- 

 bia lava. The dip of the strata on each side of the ridge toward its eastern 

 end becomes about the same, showing that the fault passes into a fold. 



Through the kindness of Mr. Frank C. Calkins, the following 

 quotations are made from his description of the same locality 

 from the manuscript of a water-supply paper now in preparation : 



The north face of Saddle mountain, where it overlooks the lower stretch of 



Crab creek .... suggests faulting in a very striking way 



It is obvious that we must have here either a normal fault with the downthrow 

 to the north or a sharp flexure, the downfolded portion having been removed 

 by erosion, leaving only the nearly horizontal strata on either side 



^Ibid., p. 96. 



