GLACIAL LAKES OF PUGET SOUND 453 



from the east to divide, one portion flowing north to the shallow 

 linear lake and thence to the Puyallup River, the other reaching 

 Ohop Creek and draining into the Nisqually River. The altitude 

 of the col is 620 feet, above which the old valley bluffs rise 350 feet. 

 It is probable that the deposits of this stream have raised the level of 

 the Kapowsin outlet. The western margin of the Puyallup Valley 

 northward toward Tacoma averages only 550 feet A.T. and Lake 

 Puyallup must have early abandoned the Kapowsin outlet and found 

 escape through spillways westward. 



With discharge by either route, the waters of the lake were tribu- 

 tary to the larger lake held back of the Chehalis-Sound divide. When 

 the ice dam failed to be effective, the Puyallup Valley became one 

 of the group of flooded troughs constituting the major glacial lake 

 of Puget Sound. 



GLACIAL LAKES OF THE SAMMAMISH VALLEY 



The Sammamish trough lies parallel to Lake Washington on 

 the east. It has its inception ten miles north of Bothel and gradually 

 deepens to its abrupt termination near Issaquah. The modern 

 Lake Sammamish, seven miles long and 35 feet A.T., lies well to the 

 south in the valley, a wooded swamp occupying the part north of 

 the lake to Bothel and a creek draining the remaining length. The 

 valley's southern portion is inclosed by three high rock hills, rising 

 1,500, 2,000, and about 2,500 feet A.T. Two low passes of pre- 

 glacial origin cross the inter-hill areas. Beetling cliffs confine them 

 in places. 



East of Issaquah, altitude 90 feet, and on the northern flank of the 

 largest of the three rock hills, is a considerable level area with an alti- 

 tude of 425 feet. Coarse gravels and cobbles of glacial drift compose 

 the surface, and are exposed in strata in several sections. Back from 

 the margin of this deposit is a terrace 20 feet higher and with a still more 

 extensive level surface continuing eastward. The face of the gravel de- 

 posit comprises the eastern wall of the Sammamish trough at Issaquah, 

 and is dissected to a depth of about 300 feet by the stream which 

 here enters from the east. Followed upstream, this creek is found, 

 four miles out of Issaquah, to be wandering through a wide, flat- 

 bottomed, swampy valley in which the stream appears incongru- 



