I'm somewhat confused.  For years, I have only heard one origin for Samuel
Clemens' pen name, Mark Twain.  This was, of course, the Mississippi River
origin.
 
However, in his book, "On the Road with Mark Twain in California and Nevada",
George Williams III states that the true origin of the name was from his
telling a bartender in Nevada to "Mark Twain"  on his tab.
 
Which of these origins is true?  I would really like to know which one it is.
 
Sincerely,
 
Rob McMonigal