In fact, four of Amtrak’s top 10 corridors (by number of passengers carried) are found here.
# 5 – San Joaquin – (Bakersfield-Oakland/Sacramento)
# 7 – Cascades – (Eugene-Portland-Tacoma-Seattle-Vancouver BC)
Both the Capitol Corridor and San Joaquin trains (and Amtrak’s long distance trains that serve Emeryville) offer connecting bus service to San Francisco over the Bay Bridge, but many Capitol and San Joaquin riders prefer to switch to BART in Richmond. The Amtrak platform is right next to BART, so a transfer is quick and painless. Discounted BART tickets are available on-board both the Capitols and San Joaquins.
In some cases the the buses run the same routes as trains when train service is not provided, For example, Thruway service is operated between Los Angeles and Santa Barbara on the Pacific Surfliners or between Seattle and Vancouver BC on the Cascades. In other cases Thruway service is provided where no train service exists at all, such as between Bakersfield and Los Angeles on the San Joaquins, between Sacramento and South Lake Tahoe on the Capitol Corridor, and between Portland and Astoria on the Cascades.
Most of the Thruway service (especially in California) is contracted for by Amtrak and operated by bus charter companies, while in other instances it may be regularly scheduled bus service provided by another company such as Greyhound.
In addition to buses, through Amtrak (provided you are also taking a train as part of the itinerary) you can reserve seats and have tickets issued on the Victoria Clipper (high-speed catamaran between Seattle and Victoria BC) or on Pacificoach bus service between Vancouver BC and downtown Victoria. (The bus leaves from the Vancouver train station, travels via BC Ferries to Vancouver Island, and continues on to the downtown Victoria bus station.) As a rule, if there is a green line on the Amtrak route map indicating other than Amtrak rail service, it can be booked and ticketed by Amtrak in conjunction with Amtrak rail travel.
Amtrak Service and Fares - navigational links
Backward to Routes - # 6 - Short-distance corridors - Central
Forward to # 8 - Service