As long as you are a passenger on Amtrak, I think you can leave your baggage with an Amtrak baggage office. I have done it a few times. Sometimes there might be a small fee. Most major Greyhound stations have storage lockers, and I would assume San Francisco would have a major Greyhound station. Portland does, and there are storage lockers there.
What I am trying to figure out: if a person arrives by train, takes the bus to San Francisco, wants to spend a day touring the city--without cumbersome baggage, perhaps catch another train later that day, what would be the best way to do that? I know San Francisco pretty well, but a lot of people do not.They not only have to leave their baggage somewhere, they have to be able to find and go back to where they left it, and get back on the bus to go back to Emeryville or Oakland to board the train. Walking around with baggage in one's hand is not the safest thing to do in a large city--even in San Francisco.
Another thing that complicates matters is that on the Coast Starlight, southbound passengers get off the train at Emeryville and take the bus from there to San Francisco. Southbound passengers from San Francisco are taken to Oakland to catch the train (not Emeryville). NOrthbound passengers leave the train at Oakland, bus to San Francisco; passengers from San Francisco are buses to Emeryville for the ride northward. There could be problems if one left one's baggage at one station rather than the other.
So, does anybody have any good, pliable suggestions about leaving one's baggage in San Francisco (or at one of the stations) so that one could spend a day sightseeing and such in San Francisco?