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Geology
The geology of the Upper Snoqualmie Basin is complex and unique in terms of the scale and extent of glacially derived sediments in the area. It is these sediments that host the aquifers in the basin. The understanding of the geologic framework in which these glacial sediments have been deposited has changed little since it was first investigated by J. Hoover Mackin in 1941. The unique aspect of the glacial history of the Upper Snoqualmie area is that it is located at the historical margins of both continental glaciers that entered the Puget Sound from Canada, and alpine glaciers that descended from the Cascade mountains. The confluence of these two glacial environments provided for large accumulations of sediment, often referred to as embankments. The sheer volume of saturated sediments in the Snoqualmie Basin, in conjunction with high precipitation (both rain and snow) is the most basic indication that a large groundwater development is plausible. More detailed studies by the EKCRWA and others have confirmed that large accumulations of sediments are present in the Basin, and that they are capable of supplying large quantities of groundwater.
This link contains an animation of the glacial advance and retreat in Puget Sound
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©2003-2007 Golder Associates
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