New 7.5-minute quadrangle maps enhance geologic understanding of the Puget Sound region. Photo: DNR
DNR’s Division of Geology has just released three new 7.5-minute quadrangle maps. Mapping in the Carnation quadrangle helped geologists clarify the relationships between different Seattle-area faults, including the Seattle fault, the Southern Whidbey Island fault, and the Rattlesnake Mountain fault. Knowing fault locations and history helps towns like Carnation and Duvall understand the context for their recent earthquake activity.
Mapping in the Lilliwaup, Skokomish Valley, and Union quadrangles provided essential information on two major issues: how polluted ground water enters Hood Canal, and the cause of frequent Skokomish River flooding. The Hood Canal mapping was done in partnership with the Hood Canal Dissolved Oxygen Program, to help find ways to improve the low levels of oxygen that hurt marine life. On the Skokomish River, geologists identified tectonic activity and uplift as recent as 15,000 years ago as a possible cause for the frequent flooding in the area.
Geologists also mapped the area’s many landslides. Furthermore, they determined that deformation near the Dewatto Valley that was formerly called a landslide was actually caused by glacial ice during the last ice age.
This newest mapping project is a continuation of last year’s work that followed faults in other areas around western Washington. All of DNR’s Division of Geology publications are now accessible online via the Publications List. To see more exciting quadrangle maps, click here.
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Tags: earthquakes, geology, map
