Puget Sound faults about 1100 years ago (AD 900—930) an earthquake of magnitude 7+ uplifted Restoration Point and Alki Point, dropped West Point (the three white triangles in the Seattle Basin on the map), caused rockslides in the Olympics, landslides into Lake Washington, and a tsunami on Puget Sound. It extends as far east as (and probably terminates at) the Rattlesnake Mountain Fault Zone (RMFZ; the southern extension of the SWIF) near Fall City. This seems geologically reasonable, as both the SWIF and RMFZ appear to be the contact between Tertiary Crescent Formation basement of Puget Sound on the west and the older
Puget Sound region Puget Sound region The Puget Sound region is a coastal area of the Pacific Northwest in the U.S. state of Washington, including Puget Sound, the Puget Sound lowlands, and the surrounding region roughly west of the Cascade Range and east of the Olympic Mountains. It is characterized by a complex array of saltwater bays, islands, and peninsulas carved out by prehistoric glaciers. The Puget Sound region has been called "Ish River country", perhaps most famously by poet Robert Sund, owing to its numerous rivers with names ending in "ish", such as the Duwamish, Samish, Sammamish, Skokomish, Skykomish, Snohomish, and the