452 J HARLEN BRETZ 



Terrace and the upper probably the original surface of the formation. 

 This filling is very similar in all features noted in the preceding 

 description to that in the Willamette valley. 



Relation of the Satsop formation to the Coast Range of Oregon and 

 Washington. — -The Chehalis and Columbia rivers cross the Coast 

 Range in capacious valleys of low gradient. In both valleys 

 the Satsop formation has been found at closely spaced intervals from 

 the coastal plain portion to the broad fillings east of the range. 

 Though not continuous across the range, the character of the 

 material of the formation, the altitudes at which it occurs, the 

 stratigraphic relations to underlying rock and to younger gravels, 

 and the topographic relations are such that there seems no reason- 

 able doubt that the deposits noted in this paper are portions of the 

 same formation. 



The Cowlitz, Chehalis, Columbia, and Willamette valleys are 

 younger than the Coast Range, and the Satsop formation is 

 younger than the valleys in which it lies. Thus the Satsop forma- 

 tion was deposited after the Coast Range had been uplifted, and 

 after its dissection was well advanced toward present maturity. 



The Satsop formation along the Columbia River in the Cascade 

 Range. — The Columbia has cut its valley across the Cascade Range 

 down almost to sea-level. This valley is a gorge about 60 miles 

 in length, only the western 35 miles of which have been mapped 

 topographically. Most of the walls of the gorge are precipitous 

 and maximum sections of 4,000 feet are available. 



Numerous bluffs along the lower 12 miles of the Oregon side of 

 the Columbia Gorge reveal a flow of gray basalt, 25-100 feet thick, 

 in the Satsop formation. The Satsop rises northeastward in the 

 walls of the gorge about 90 feet to the mile, bringing its base 900 

 feet A.T. in the salient known as Angels Rest (Fort Rock) and 

 exposing the Columbia River lava below the Satsop. Many sections 

 along this distance show an unconformable contact between the Sat- 

 sop and the underlying basalt, and some of them show the upper 

 10-20 feet of this basalt to be very much decayed, far exceeding the 

 decay of the basaltic pebbles in the lower part of the Satsop. In 

 the section at Angels Rest the Satsop (including the intra- 

 formational lava) is 500 feet thick. A second lava-flow appears in 



