I just had a thought, while looking over Twain's railroad experiences, 
that his remarks in Roughing It regarding California climate are 
actually derived from his Pilgrim's Life Tour rather than his life in 
San Francisco during the Roughing It days.  He took the Central Pacific 
Railroad from Sacramento to Donner Pass April 23, 1868.

-- 
/Unaffiliated Geographer and Twain aficionado/