312 



University of California. 



[Vol. 2. 



The southerly inclination of this bed and its broken character on 

 the south side of the valley indicate that considerable movement 

 has taken place in post-Rattlesnake time along the plane of the 

 fault which has broken the Columbia lava at this point. This 

 movement is a continuation of that which had given the Mascall 

 formation a southerly dip before the Rattlesnake was deposited 

 upon it. 



South of the Blue Mountains, according to Osmont, the rhyo- 

 lite flow appears again in its typical form and rests upon the Mascall 

 formation. 



The present drainage of the John Day must have been estab- 

 lished before the tilting of the Rattlesnake took place, as the river 

 now turns sharply to the north at Picture Gorge, leaving the soft 

 deposits of Mascall and Rattlesnake, which extend farther to the 

 west in the direction which the stream has run for many miles, 

 and cutting straight through the Columbia lava monocline. 

 Had the movement taken place before the cutting of this gap was 

 initiated, the river would probably have been thrown toward the 

 southern side of the valley and would never have come out at this 

 point. 



Age of the Rattlesnake. — Without making any attempt at exact 

 correlation of the Rattlesnake with any other formation, there 

 seems to be sufficient evidence to show that it should be consid- 

 ered as belonging to the Pliocene of the standard scale; perhaps it 

 represents only the later portion of that period. Its stratigraphic 

 relations to the Mascall formation are such that it could not be 

 older than early or middle Pliocene, while the amount of erosion 

 which took place between the close of this epoch and the middle or 

 latter part of the Quaternary shows that it could not possibly be 

 later than Pliocene. 



QUATERNARY. 



Terraces. — At numerous points along the John Day and its 

 tributaries, one or more terraces are to be found not far above the 

 existing floor of the valley. At the upper end of Haystack Valley 

 on the main John Day, gravels containing numerous large rounded 

 pebbles of rocks not outcropping in that neighborhood are exposed 



