454 J HARLEN BRETZ 



strikingly like that along the Sandy River, just west of the range. 

 This is true of its composition, its structure, its degree of weathering 

 and of cementation. It differs in having no lava-flow within the 

 formation. 



Between Hood River and The Dalles, the Columbia River has 

 cut across two anticlinal ridges, each rising more than 2,000 feet 

 above the stream. Each anticline is composed almost wholly of 

 Columbia River lava. Each carries patches of a sedimentary 

 formation composed chiefly of volcanic detritus, but containing 

 much rounded gravel in which basalt, granite, and quartzite are 

 present. 



In the vicinity of The Dalles is a stratified deposit of volcanic 

 agglomerate, tuff and ash, with strata of river sand and gravel, 

 1,000 feet thick, and capped by a flow of gray basalt. The western 

 margin of the deposit is uptilted on the flank of the eastern anti- 

 cline. Though no pebbles of quartzite or granite were found 

 during the brief examination possible, it seems probable from 

 stratigraphic evidence that the deposit at The Dalles is a local phase 

 of the Satsop formation. 



The Satsop formation between the Columbia and Yakima valleys. — 

 The Simcoe Range is a prominent eastward spur of the Cascades, 

 extending some 50 miles east of The Dalles, and separating the 

 lower Yakima valley from the Columbia valley to the south. The 

 range is structurally a broad anticlinal fold. Typical Satsop 

 quartzite gravels, resting on dense black basalt and covered by 

 gray basalt, lie in many places on the southern slope. The highest 

 altitudes at which these gravels are known to occur in the Simcoe 

 Range is 4,000 feet. The overlying lava does not extend far down 

 the northern slope of the range, and the Satsop formation on this 

 slope, unprotected by a lava cap, consists only of scattered quartz- 

 ite cobbles and pebbles. All other materials in the original deposit 

 have been destroyed by weathering. Quartzite pebbles were 

 found as far north of the range as the southern part of the Ellens- 

 burg quadrangle. There are areas within sight of the Yakima 

 River where these pebbles cover 50 per cent or more of the surface. 



The Yakima basalt in the Ellensburg quadrangle (probably the 

 equivalent of the Columbia River lava) is overlain by the Ellens- 



