SALIENT FEATURES OF THE GEOLOGY OF OREGON 93 



Knoxville fauna, including a number of well-known species. The 

 latest, or Chico, flora is not well represented in Oregon but is in 

 closer agreement with the invertebrate faunas. 



CENOZOIC 



Eocene. — Marine Eocene is known to comprise parts of the 

 Coast Range^ of Oregon from Rogue River northward to the Colum- 

 bia, being well developed along their western flank within the Port 

 Orford and Coos Bay quadrangles, and along their eastern flank 

 within the Roseburg Quadrangle. These sediments outcrop along 

 the western base of the Cascades east of Roseburg and at several 

 localities within the Willamette Valley. 



The Eocene rocks consist of sandstones, shales, carbonaceous 

 shales and coals, conglomerates, tuffs, basalts, and various intru- 

 sives. 



The Umpqua-Arago^ group, including the marine and estuarine 

 deposits, may represent over 20,000 feet of sediments, which are 

 divided into a number of formations, the exact positions in the 

 geologic column of several of which are as yet uncertain. The 

 oldest, the Umpqua group, is well developed on Little River, 

 Roseburg Quadrangle, where it consists of 7,500 feet of marine sed- 

 iments. This group includes the Wilbur tuff — lentils, the Umpqua 

 formation, the Tyee sandstone, and possibly the Oakland lime- 

 stone formations. The most important of these is a rather coarse- 

 grained, thick-bedded sandstone known as the Tyee sandstone. 

 This has been traced by Washburne^ from Rogue River Mountain 

 northward along the Coast Ranges into Tillamook County. 



The Arago, the lower part of which may be the equivalent of a 

 part of the Umpqua formation and the later Tyee sandstone,"" 

 is found within the coast quadrangles and consists mainly of sand- 

 stones and shales, some of which are coal-bearing. The older 

 Pulaski formation also includes some fossiliferous limestone and 

 basaltic tuffs. The younger Coaledo formation is coal-bearing, 

 but along the eastern margin of the field includes some basaltic 



I S. Diller, U.S. Geol. Surv., 17th Ann. Kept., Part I, p. 469. 

 ^ Ibid., Folios 49, 73, and 89. 



3 C. W. Washburne, U.S. Geol. Surv., Bull. 590, p. 9. 

 "R. E. Dickerson, Proc. Cal. Acad. Sci., Series 4, IV, 114. 



