THE SATSOP FORMATION OF OREGON AND 

 WASHINGTON 



J HARLEN BRETZ 



University of Chicago 



The name "Satsop" was given by the writer 1 in 191 5 to a 

 deposit of stream gravels in the Chehalis valley of western Wash- 

 ington. The deposit was known then to extend throughout most 

 of the length of this valley and to occur only in dissected terraces of 

 stained and decayed gravel standing high above the valley floor. 

 So far as then known, the Satsop formation rested unconformably 

 on Eocene and Miocene marine sediments. Because of this rela- 

 tionship and because of its limitations as a valley filling, it was 

 thought to be of Quaternary age. 



Two field seasons have since been spent in the study of this 

 formation in Washington and Oregon. It has been found in places 

 along almost the entire Pacific coast line of Washington and along 

 the Columbia River valley from the Pacific to the great lava plain 

 east of the Cascade Range. It has been identified from the litera- 

 ture along the coast of Oregon. Its relations to the Coast Range 

 and the Cascade Range are very different, and constitute the chief 

 reason for the appearance of this paper. 



The Satsop formation in the Chehalis valley. — The river gravels 

 which constitute the Satsop formation of this valley exist along 

 the lower 60 miles of its total length of 85 miles. The formation 

 extends back up several tributary valleys, the type sections occur- 

 ring in one of these, the Satsop valley. The maximum known 

 thickness is 300 feet. The formation is composed of local materials 

 and is stream-bedded with dip down the present drainage lines. 

 Dissection has reduced the formation to a series of terraces, and 

 decay has produced a residual loam on the surface of the highest 



1 J H. Bretz, "Pleistocene of Western Washington," Bull. Geol. Soc. Am., XXVI 

 (1915), 131. 



446 



