Wash. Rev. Code § 47.17.175
A state highway to be known as state route number 104 is established as follows:
Beginning at a junction with state route number 101 in the vicinity south of Discovery Bay, thence southeasterly to the vicinity of Shine on Hood Canal, thence crossing Hood Canal to a junction with state route number 3 in the vicinity of Port Gamble; also
From that junction with state route number 3 in the vicinity of Port Gamble, thence to Port Gamble, thence southerly and easterly to the state ferry terminal at Kingston; also
From the state ferry terminal at Kingston via the state ferry system easterly to the state ferry terminal at Edmonds; also
From the state ferry terminal at Edmonds, thence southeasterly to a junction with state route number 99 in the vicinity of the Snohomish-King county line; also
Beginning at a junction with state route number 99 in the vicinity of the Snohomish-King county line, thence southeasterly to a junction with state route number 522 in the vicinity of Lake Forest Park.
RCW 47.17.175