For some of the earliest bus companies, listed in early reports of the California Railroad Commission, a first year or decade of operations is listed.
Additional bus companies, listed as existing during additional years or decades, are mentioned in old City Directories, and in the WPA American Guide Series of state guidebooks.
Coniglio Auto Stage - existed in 1952, served Pittsburg and vicinity.
Atkinson Transportation Co. - existed in 1942, served Martinez.
Martinez-Benicia Bus Line - existed in 1942.
Martinez-Concord Bus Line - existed in 1942.
Pettas Auto Stage - began operations by 1920's, served Pittsburg, Columbia Park and vicinity.