At the western end of the Barbary Coast, on the corner of Pacific Street and Columbus Avenue, Mary Ellen Pleasant did what Rosa Parks would be given wide acclaim for: in 1866, as she tried to board an omnibus, the driver prevented her from entering. She sued the company and won $500 plus a promise to allow blacks to ride public transportation.

That's the extreme, bare-bones version. The Wikipedia link does a much more thorough and entertaining job of presenting Mary Ellen's information.

I'd certainly never heard of her .. why not? One thought is that although she was hugely influential in Gold Rush San Francisco and later, it was a smear campaign waged against her in her later years that overshadowed her lifetime's accomplishments. Yellow journalism publications of the time were widely read and believed. It is only recent discoveries of contemporary accounts that tell another point of view that are allowing Mary Ellen's achievements to become more well-known.