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

Chris Iacoboni

Whitman College, Walla Walla, WA 99362


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.