"The only delta of Vashon age known in the valley of Hoods Canal is at the mouth of the Dusewallips (sic) River, on the north side of the valley. At the seaward upper margin, it is 120 feet above the Sound. Its surface is a plane, sloping towards the troughs of the Hoods Canal. Its altitude makes it obviously a feature produced subsequent to (glacial) Lake Hood, whose waters were 100 feet higher." J Harlen Bretz (1913)
Deltas played a major role in Bretz's study of the Puget Sound's glaciated history, especially when it came to determining the probable boundaries of the many glacial lakes that formed as the Puget Lobe retreated northward up the Sound.
Deltas are formed when a river or creek enters a slower moving or standing body of water. The deposition of sediments that results from the energy transaction typically expresses itself as a wedge shaped mass, with its tip facing in the overall direction of flow, resulting in the characteristic shape seen above.