Built in 1942 by Sacramento River Lines at Sacramento, Calfornia as the Plumas for in-house use.

In 1970 she was acquired by the Seattle Disposal Company of Seattle, Washington, where the tug retained her name.

In 1984 the tug was acquired by the Fremont Tugboat Company of Seattle, Washington, where she was renamed as the Sovereign.

In 2006 she was sold to an individual and transferred to Washington State Registration under the name Mollusk.