Were John Muir and Mark Twain ever in the same place at the same  time?
 
Muir was close enough in age (2 1/2 years younger) for them to be  
contemporaries, but without going too deep into research, a parallel  review of a 
timeline of Twain, and the timeline for John Muir's life (as  given at: 
http://www.sierraclub.org/john_muir_exhibit/john_muir_day_study_guide/biographical_
timeline.aspx ),   suggests they did not ever cross trails.
 
Bob Stewart