the gardens are broken up into various themes - chinese garden, rose garden, etc. - and the provided map outlines where everything is located. sadly the japanese garden is currently under construction, as they're gearing up for their 100th anniversary with a 2012 extravaganza.
and a few snaps at the chinese garden:
the huntington library, art collections & botanical gardens
1151 oxford road
san marino, CA 91108http://www.huntington.org/