For the full story of “Captain Brown” and the Cocos Island treasure I highly recommend The Voyage of the Herman, by Theon Wright and Ione Ulrich Sutton (1966). It’s quite a yarn!
Actually, however, it isn’t quite “all” the story. Because the authors didn’t know about the excessively rare Our Search for the Missing Millions (of Cocos Island), by “One of the Searchers” [John Chetwood] (1904). The names of the players were changed - my copy has “Brawn” crossed out and “Brown” written in. In another copy it was done with a little rubber stamp.
San Francisco was the port from which a great many Cocos Island treasure hunts were launched. They are covered in many newspaper articles. It’s not a coincidence that they were generally published on Sunday
Dig for Pirate Treasure, Robert I. Nesmith (1958) has a reliable chapter on the entire history of the Island. It is closed to treasure hunting today by the government of Costa Rica.
Good luck to all,
The Old Bookaroo