If you research the the timetables of the first two years of Amtrak you'll find some interesting operations. First, trains #12 and 13 operated daily between Oakland and San Diego as the COAST DAYLIGHT. At the same time, #11 and #14 operated three times a week as the COAST STARLIGHT between Seattle and San Diego. Secondly, you will find trains # 5 and 6 operated daily between Chicago and Denver as the DENVER ZEPHYR and the same train numbers operated three times a week between Chicago and Oakland as the CITY OF SAN FRANCISCO. Essentially there was an extension of the COAST DAYLIGHT and DENVER ZEPHYR three times a week.