If your flight departs from T1 then, yes, you will need to go to staff travel in the Queens building in the departures level, down the corridor from Premier Check-in and around the corner.
This only applies to
LONG HAUL destinations.
San Francisco and Los Angeles are the US destinations served by Terminal 1 (other long-hauls are Vancouver, Tokyo, Hong Kong and Johannesburg ).
For short-haul staff travel, you check in at the "Wendy House" in Zone East (up in the corner where UK Domestic flights check in). Your bags get sent down and you go to the gate for onload.
For all BA staff travel, it is now essential that you are listed prior to check in. There are self-service computers at Staff Travel in the Queens Building or in Zone East by the Wendy House to enable you to list if you hadn't done so previously.
Hope this helps and enjoy the strength of the Great British Pound while you're in the USA!