Wash. Rev. Code § 47.17.085
A state highway to be known as state route number 21 is established as follows:
Beginning at a junction with state route number 260 in Kahlotus, thence northerly by the most feasible route, crossing state route number 26, and continuing northerly to a junction with state route number 395 in the vicinity of Lind; also
Beginning at a junction with state route number 395 in the vicinity of Lind, thence northerly by the most feasible route by way of Odessa to a junction with state route number 2 in the vicinity west of Wilbur; also
Beginning at a junction with state route number 2 at Wilbur, thence northerly by the most feasible route to a junction with state route number 20 at Republic; also
Beginning at a junction with state route number 20 east of Republic, thence northeasterly by the most feasible route to the east of Curlew lake by way of Curlew to the international boundary line in the vicinity of Danville.
RCW 47.17.085