192 GUIDEBOOK OF THE WESTERN UNITED STATES. 
Below the point of junction the stream is known as Duwamish 
River, and this the road follows to the tidal flats of Elliott Bay at 
Seattle. 
The broad valley at Auburn is distinctly different from the ordinary 
stream valleys of this region, in that it is wider than is required by 
such streams as now occupy it, it is flatter than valleys excavated by 
erosion, and it is open to tidewater at both ends—Elliott Bay (Seattle) 
on the north and Commencement Bay (Tacoma) on the west. The 
floor of the valley is so flat that streams entering it build delta-like 
accumulations of sediment upon which the stream channel shifts 
from place to place. White River, next to Green River on the 
south and named because of the milky color of its water, derived 
from the glaciers of Mount Rainier, enters the valley a few miles 
above Auburn. Part of the stream at times turns south into Puyal- 
lup (poo-yal’up) River and reaches tidewater at Tacoma and the other 
part flows north and unites with Green River. The arrangement of 
the valleys and their peculiar connection with bays and similar in- 
dentations of the coast line strongly suggest that at one time this 
entire valley from Tacoma to Seattle was an arm of the Sound simi- 
lar to but smaller than Admiralty Inlet and that it has become a 
land valley simply by being filled with sediment brought down by 
the rivers from the Cascade Mountains. 
Bailey Willis, who has made a careful study of the Puget Sound 
region, is of the opinion that the peculiar branching channels of the 
Sound could have been produced only by the submergence of a land 
on which a branching river system had formerly existed. If this 
view is correct, it is evident that many modifications must have been 
made, for a peculiarity of the channels of the Sound is that they not 
only unite as the tributaries of a river system unite, but they separate 
ina most intricate fashion. Taken as a whole, the conclusion appears 
well founded, but there are many minor points that still remain to 
be explained. 
to fill the deep depressions, so that when 
free of ice these were occupied by marine 
ntorg'! 
and covered by the deposits of ie phe. 
ciers mentioned above. 
Beneath these sands and gravels lie 
deposits of stiff blue clay, mostly strati- 
fied but locally filled with subangular 
posits, 
deposited by the Admiralty glacier, 
were laid down during an earlier stage 
of glaciation, when the Puget Sound 
asin was occupied by a lobe of the 
Cordilleran ice sheet, as at the Vashon 
stage. There are some suggestions that 
still earlier glaciers occupied the basin, 
but these are too indefinite to be given 
much weight. 
