172 GEORGE OTIS SMITH 



country about the upper portion of the Naches was only seen from a dis- 

 tance, however, and may have a more complete structure than is here 

 suggested. 



Here again the later field study has afforded conclusive evi- 

 dence that the Cleman mountain anticline is complete, except for 

 a distance of six miles along its southern slope, where a huge 

 landslide has pushed into the canyon of Naches river below. 

 However, it is along the lateral escarpment facing this landslide 

 area that the best exposures of the structure are to be had. 



Umptanum ridge succeeds Cleman mountain on the north, 

 Wenas valley separating the two. North of this in turn is Man- 

 astash ridge, known also as the Beavertail hills. The recon- 

 noissance description of this region follows : ^ 



The rocks on the head waters of Wenas creek are Columbia lava, broken 

 and upturned in fault scarps, which merge into a general region of uplifts to 

 the west, but become separated and well defined in traversing the desert 

 country to the east. The ridges thus found agree in their principal features 

 with nearly all the east and west ridges in Yakima and Kittitas counties. 

 One of the lines of east-and-west faulting between Wenas and Kittitas val- 

 leys is marked by Umptanum ridge, which presents its bold escarpment to 

 the northward. North of this, again, are the Beavertail hills, which are also 

 a monoclinal uplift. 



Umptanum ridge is perhaps the highest of these east-west 

 ridges where it is crossed by Yakima river. The perfect arch of 

 the ridge at Umptanum gap exposes a thickness of Yakima 

 basalt exceeding 2,000 feet. The anticlinal structure is most 

 evident, the fold being unsymmetrical, with the northern dips 

 steeper. If any faulting is present, it must be of the nature of 

 displacement on the plane between two sheets of basalt, but in 

 any event, judging from the excellent section seen in Umptanum 

 gap, faulting is of minor importance. Along the northern face 

 of the ridge farther west there is a prominent outcrop of black 

 basalt making a scar somewhat suggestive of a bedding fault. 

 At another point, however, an even more prominent feature of 

 this sort was seen in section, and the observation was conclusive 

 as to the absence of any faulting. Thus, on the evidence of 

 detailed study, the assertion is confidently made that in no 



^Ibid. 



