Foss Peak is a 6,524 ft summit in the Tatoosh Range which is a sub-range of the Cascade Range. It is located south of Mount Rainier within Mount Rainier National Park, in Lewis County of Washington state. The peak is named for Thea Foss (1857-1927) who founded the Foss Maritime Company with her husband in 1889. The peak also has an alternate name, Manatee Mountain. The nearest higher neighbor is West Unicorn Peak, to the southeast. Precipitation runoff from the mountain drains into tributaries of the Cowlitz River.