I’ve led a sheltered life - I’ve never seen a large key before.

Looking online, there are images for church keys, gas keys, large skeleton keys, etc. Our object certainly could be just one key.
The photo doesn’t adequately show the object. It is mostly flat on one side except for the top part where it is still flat but appears to have been twisted down a wee bit. The bottom half is of course more solid, wider and it is “thicker” than the top half.
It may not even be a family item. Perhaps it was found in San Francisco’s Golden Gate Park where one ancestor worked or found by another relative who was a motorman in San Francisco. Maybe originally the item had a note with it or maybe everyone in the extended families knew where it came from so no note was needed.
Thank you again for your advice, Erato. It is very helpful.