Breathtaking, when you think of it: within living memory there were three San Diegan round trips a day to and from LA, making only Fullerton, Santa Ana, Oceanside, and Del Mar, plus an all-stops local, and no commuter service at all. Between Santa Ana and San Diego there were three controlled sidings (or maybe two main tracks). One San Diegan trip in each direction included a reserved-seat coach for El Capitan passengers to and from the east; the whole service appeared to be focused on Chicago connections.
Fun fact: when the Coaster service was in the planning stage the good burghers of Del Mar made it clear that they did not want commuters cluttering up their station, so the planners went north to sound out Solana Beach. The reaction there was "you want to stop your trains here? So we'll have train service, and commuters can park here, and maybe buy some things in town on their way home? Great! When can it start?" So Solana Beach became a Coaster stop, and Amtrak, in keeping with its policy of sharing stations with local transportation, announced that Amtrak trains would henceforth stop at Solana Beach instead of Del Mar since it made no sense to have two stops so close together. Del Mar travelers who had been accustomed to taking Amtrak when they went to LA were not happy, but it was too late by then.