454 J- HARLEN BRETZ 



ously small and ineffective. The valley floor here is about 50 feet 

 higher than the gravel deposit with which it doubtless correlates. 



At Preston, this old floor suddenly ends at 540 feet A.T., with 

 the valley at full width. A descent of about 100 feet occurs to Raging 

 River which comes in from the southeast and turns north at this 

 point. But the level of the valley floor at Preston is continued, in 

 the form of terraces, up the Raging River for four or five miles to 

 the point where the grade of the stream has brought it up to the level 

 of the Preston Valley. 



At the time that Raging River was discharging into the Samma- 

 mish depression, it seems probable that an ice tongue occupied the 

 trough, and held back the river to the level of the deposit referred to 

 above. This deposit, hardly to be considered as a delta, is the oldest 

 record of glacial waters in the Sammamish Valley. 



A glacial lake of limited extent must have succeeded the ice tongue 

 in the southern portion of Sammamish Valley, and discharged south- 

 ward through the rock-walled valleys noted, both of which are 

 floored with coarse, rounded gravel. The lowest altitude at which 

 this lake could have existed with these discharge-ways is about 315 

 feet. 



A channel exists across the till ridge between lakes Sammamish 

 and Washington at the north base of Newcastle Hill, the lowest of 

 the three rock hills noted. It is floored with coarse gravels. Another 

 channel a mile north of the one just noted contains Phantom and 

 Larsen lakes, and is floored with swamp deposits. Both are about 

 300 feet A.T., and must have existed contemporaneously or nearly 

 so with the southward escape. 



A third abandoned channel across the till ridge between the two 

 parallel valleys exists near York, or Willows, a few miles north of 

 Redmond. The summit of the York channel is 160 feet A.T. and 

 no perceptible slope exists in the swampy bottom to the west. This 

 fact argues a similar level of ponded water in the Lake Washing- 

 ton valley. Lake Washington's surface today is 130 feet lower than 

 the col. 



Correlating with the York channel is the highest level of the Red- 

 mond delta, a heavy gravel deposit which lies a mile east of the town 

 of Redmond. This delta occurs at the debouchure of a former chan- 



