PRESENT MINOR TOPOGRAPHIC FORMS. IDB 
Flood plains and deltas—At their debouchures from the marginal 
ravines of the plateaus, those streams which enter alluvial plains build 
cones, and those which empty into tidewater tend to construct deltas. 
The alluvial cones are generally composed of gravel and coarse sand. 
They are of moderate size and are noticeable chiefly as areas of material 
coarser than the alluvial silt with which they merge. 
White river, a stream draining the largest glacier system of mount 
Rainier and entering the Duwamish valley nearly due east of Tacoma, 
presents peculiar features of alluvial accumulation and stream adjust- 
ment. Ata point in its gravel-banked gorge 2.5 miles (4 kilometers) 
east of the eastern edge of the Duwamish valley the river divides into 
two branches, which continue on distant courses, known as White river 
and Stuck river, to tidewater, and empty 23 miles (89 kilometers) apart. 
For 2 miles (3.2 kilometers) from their parting the branches diverge but 
slightly ; but thence the one flows northward to Elliott bay near Seattle, 
whereas the other, Stuck river, turns southward and, joining the Puyal- 
lup, discharges into Commencement bay opposite Tacoma. Des Moines 
island, which is shown on the map, plate 7, lies between the two mouths. 
The point of divergence is about 160 feet (48 meters) above tide. The 
distance to the northern mouth at Seattle is 23.5 miles (87.6 kilometers) 
along the axis of the valley and 37.5 miles (60 kilometers) by the river’s 
course. By the southern branch to the Puyallup is 8.5 miles (14 kilo- 
meters) along the valley’s course, and to the delta front in Commence- 
ment bay 16 miles (25 kilometers). Both northward and southward the 
Duwamish valley is filled with alluvial silt, such as the White and 
Puyallup rivers now carry from the glaciers and with which they are 
extending their deltas. Throughout their courses White and Stuck 
rivers flow between steep banks of alluvium, 5 to 15 feet (1.5 to 4.5 
meters) high above the average water level of the streams and slightly 
higher than the plain toward the sides of the valley, where marshy 
ground occurs. Thus the streams meander through typical flood plains. 
The topographic type represented by the divergent arms of White river 
and their flood plains is that of an alluvial cone merging into a delta, 
recognizable as a simple, consistent form when traced up from either 
mouth to the parting of the arms, although they embrace the older 
feature, Des Moines island. 
From the head of the alluvial cone, where the arms separate, to the 
deltas this peculiar river formation is at the present time in vigorous 
development. It is nowhere yielding, but in each phase is growing. 
From the data on the topographic map its slopes have been determined 
as follows : 
