THE SAT SOP FORMATION 



453 



this section, capping the Satsop gravel and con- 

 stituting the surface formation back from the 

 edge of the Columbia Gorge. It may be traced 

 along the cliffs to a volcanic cone known as 

 Devils Rest, overlooking the gorge but a little 

 back from the bluffs. Devils Rest is one of 

 a dozen or more such cones near the gorge 

 which have supplied the lavas overlying the 

 Satsop formation. 



The accompanying section (Fig. 2) tells the 

 rest of the story better than would a detailed 

 description. The intra-Satsop flow does not 

 appear elsewhere in the range, but volcanic 

 fragmental material is prominent in most sec- 

 tions of the formation. All phases of this 

 material are present, from ash and lapilli to 

 volcanic bombs, rudely stratified by their fall; 

 from slightly water-rolled and poorly sorted 

 debris to well-worn pebbles and cobbles of 

 the gray lava, associated with equally worn 

 pebbles of Columbia River lava and beautifully 

 smoothed and polished pebbles of quartzite. 



The Satsop deposit invariably rests on 

 eroded Columbia River lava (a dense black 

 basalt) and is capped by flows of gray basalt. 

 In places the Satsop is absent and the two 

 lava formations are in contact. The highest 

 altitude at which the Satsop formation has 

 been found in the Cascade Range is 3,700 feet 

 A.T. in Benson Plateau midway across the 

 range. Its thickness here is nearly 700 feet. 



On the eastern slope of the main range the 

 river phase of the Satsop (i.e., well-stratified 

 gravel composed predominantly of basalt and 

 quartzite) appears at 2,500 feet and descends 

 eastward to 100 feet A.T. in the synclinal 

 Hood River valley. The formation in this is 



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