Geomorphology of the Saddle Mountain East Fault, Olympic Peninsula, Washington

Chris Iacoboni

Whitman College, Walla Walla, WA 99362

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Eleven hundred years ago, an earthquake at the Saddle Mountain East fault created Price Lake by damming a valley with the upthrown fault block. The Saddle Mountain East fault was the first known active fault in Washington, discovered in the 1970s. Today, a team of researchers is applying new paleoseismic techniques to the fault; we are currently making detailed measurements along the fault scarp, coring lake and adjacent wetland sediments, and making magnetic surveys. The goal of the research is to determine: i) what portions of the intermittent compound scarp are an expression of structure vs. mass wasting; ii) the relationship between the Saddle Mountain East fault and the Cushman “Rift,” which may be a graben whose genesis is controlled by the fault; iii) what the history is of the fault before 1100 B.P.; iv) why the outlet of Price Lake, where the fault dams the valley, does not line up with the fault on maps.