Here is a 9,933-square map of California and most of Nevada.  I exaggerated 
the plains and rivers in the desert areas for playability.  The mountains 
all represent real mountains at least 8,000 feet high.  I selected which 
rivers to show based more on location (playability) than size.  Note that 
units may walk across (not realistic) several points of San Francisco Bay, 
but if I separate the land more, it is impossible in the game to build 
bridges across them.  Perhaps the units get across by raft or canoe. 

Feel free to distribute this, or altered versions, however you want.

--Otis, a native and resident of California