I mapped Sam's journey from Keokuk to New Orleans, via Chicago and 
Cincinnati, for those of you interested in such things.  Any commentary 
is from the Mark Twain Project's collection of letters and editorials.  
I'm still trying to sort out the history of the railroads involved.  I'm 
discovering just how corrupt the development of railroads was.

http://twainsgeography.com/content/starting-out-amazon

If anyone knows of commentary on Sam's first trip with Horace Bixby I'd 
appreciate a lead on it.  About all I know is Sam got aboard the Paul 
Jones in Cincinnati, ran aground near Louisville, dropped of armaments 
at Baton Rouge and discovered that passage to the Amazon was not 
immediately available fro New Orleans.