Alvin,

  I found some evidence that Mark Twain did, in fact, know Bierce in San
  Francisco in 1865.  But judge for yourself how well; I quote a section
  from SLC's Autobiographical Dictation of June 13, 1906 concerning his
  San Francisco days on the "Morning Call":

  "...I spent a good deal of time with Bret Harte in his office after
  Smiggy McGlural came, but not before that.  Harte was doing a good deal
  of writing for the CALIFORNIAN - contributing "Condensed Novels" and
  sketches to it and also acting as editor, I think.  I was a
  contributor.  So was Charles H. Webb; also Prentiss Mulford; also a
  young lawyer named Hastings, who gave promise of distinguishing himself
  in literature some day.  Charles Warren Stoddard was a contributor.
  Ambrose Bierce, who is still writing acceptably for the magazines
  today, was then employed on some paper in San Francisco - THE GOLDEN
  ERA, perhaps.  We had very good times together - very social and
  pleasant times.  But that was after Smiggy McGlural came to my
  assistance; there was no leisure before that..."  (See: _Mark Twain in
  Eruption_, 261-262)

  There is another brief reference to Bierce in A.B. Paine's _Mark
  Twain's Autobiography_, Volume 1, pg. 154.   This reference (probably
  written by Clemens in 1898) indicates that Bierce was part of the
  "young literary" group that worked on the GOLDEN ERA.

Paul Berkowitz