Kosmos was an unincorporated community in Washington State. It was established in 1904 with a grocery store and a post office. Kosmos reached its peak in the 1940s, when mills and logging camps dotted the landscape. Residents relocated from Kosmos in advance of the completion of the Mossyrock Dam in 1968. Before the Cowlitz River rose behind the dam and formed Riffe Lake, contractors razed most structures, except for their foundations. Occasionally, periods of low water expose the remains of the town.