112 University of California. |yo&. 3. 



lower than those to the east."* To the north and south of 

 Antelope tnese ridges die out and merge into the great basalt 

 plateau extending to the Des Chutes River. 



The John Day Basin itself contains an enormous accumula- 

 tion of Tertiary sediments, which in post-Tertiary time have been 

 deeply dissected bv the John Day River and its tributaries. The 

 area is therefore characterized by hills and plateaus separated by 

 deep canons or narrow valleys. 



The region probably has been defined more or less clearly as 

 a basin of accumulations since the beginning of the Cretaceous 

 period. It has, however, suffered frequent crustal disturbance, 

 as shown by the increasingly disturbed altitudes of the forma- 

 tions observed as we descend the geological scale. In late 

 Tertiary time, the northeastern and southeastern limits of the 

 basin were obliterated, perhaps by volcanic accumulations, to be 

 revealed subsequently by the forces of erosion and by renewed 

 activity on the main lines of crustal movement . 



The main characteristics of the geological formations, in order 

 of age, will now be briefly sketched. 



Pre- Tertiary Geology. — In its broadly general features, the 

 pre-Tertiary geology of the Blue Mountains has a noteworthy 

 similarity to that of the Sierra Nevada in Northern California. 

 Corresponding to the "sub-jacent series" of the Sierras, they are 

 clay slates and metamorphic sandstones intruded by plutonie 

 rocks of granitoid and of ultrabasic character. Overlying this 

 ancient series are Cretaceous shells, sandstones and conglomer- 

 ates, corresponding in lithological character to the Knoxville and 

 Chico formations of this State. In the upper Cretaceous are 

 found an abundant fossil fauna which clearly define its age as 

 lower Chico.* 



The more ancient rocks were observed in the Blue Mountains 

 south and east of the Basin, and the Cretaceous in the foot-hills 

 of the southern ridge, where the Chico has transgressed across 

 the supposed Knoxville. 



The Clamo Eocene. — The Eocene is generally exposed, and 

 probably reached its greatest development in the western end 



* Loe. eit., p. 271. 



T. W. Stanton, quoted by Merriam, op. cit. p. 281. 



