The Cowlitz River once carried anything set afloat near its headwaters beyond Packwood past this point to the Columbia River and eventually the Pacific Ocean, and Native Americans and pioneers used it both as a transportation route for themselves and their products and as a food source from the yearly salmon runs that migrated upstream to spawn. The area now covered by Riffe Lake had once been the site of the pioneering communities of Riffe and Kosmos, whose last remnants were flooded in 1968 by construction of Mossyrock Dam along the Cowlitz. Riffe was established in 1898 on the Floyd L. Riffe homestead five miles southwest of Morton, and in 1904 Charles W. Hopkinson built a sawmill and established a post office, creating Kosmos. Riffe and Kosmos reached their heyday in the 1940s, when local railroad-tie mills and logging companies thrived.