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 melting retreat of the Vashon Glaciation eroded the land, creating a drumlin field of hundreds of aligned drumlin hills. Lake Washington and Lake Sammamish (which are ribbon lakes), Hood Canal, and the main Puget Sound basin were altered by glacial forces. These glacial forces are not specifically "carving", as in cutting into the landscape via the mechanics of ice/glaciers, but rather eroding the landscape from melt water of the Vashon Glacier creating the drumlin field. As the ice retreated, vast amounts of glacial till were deposited throughout the Puget Sound region. The soils of the region, less than ten thousand