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
Lake Kapowsin Lake Kapowsin Lake Kapowsin is a lake in Pierce County, Washington, about halfway between Tacoma on Puget Sound, and Mount Rainier in the Cascade Mountains. The lake is long and wide, lying in a channel formed by meltwater from the Puget lobe of the Vashon glacier during the Pleistocene glaciation. A small unnamed island lies in the northern half of the lake. As indicated by a drowned forest in the lake and other evidence, the Puyallup River was inundated about 550 years ago by a lahar from Mount Rainier called the Electron Mudflow. The mudflow partially filled the channel (leading