Additional bus companies, listed as existing during 1930's, are mentioned in the WPA American Guide Series of state guidebooks.
For some of the earliest bus companies, listed in early reports of the Washington Department of Public Works, a first year of operations is listed.
Evergreen Bus Line - served Camas, Washougal.
Yacolt Stage Co. - began operations in 1921, served Vancouver, suburbs.
Yacolt & Yakima Motor Coach Lines - existed in 1930's.