CALIFORNIA
we've got some real good ones...
Ryan Hall
Tim Danielson (3:59 mile in hs)
Mac Fleet
AJ Acosta
German Fernandez
Michael Granville (1:46 natnl hs record)
Mike Stember
Curtis Beck
Eric Hulst
the answer of the OP's question largely depends on what you mean by 'best'-
i think that German Fernandez is the most talented runner in CA history- 14:24 at woodward park, 4:00/8:34 double at the state meet, then winning NCAA 1500 setting NCAA indoor mile record and setting junior 5k record all in his freshman year of college. unfortunately since then his career has been put on hold by injuries.
Ryan Hall is probably the most 'accomplished' given that he has made 2 Olympic teams and has run a 2:04 american record marathon. also fun fact he set the state meet record at 4:02 for 1600 his senior year (2001)
Mike Stember is a good candidate- he set the state meet record in the 1600 (amazing video if you haven't seen it, i believe it is 1995 or 1996) in 4:04 by closing in 1:56 as a junior and went on to become an all american at stanford and make the 2000 olympic team in the 1500
Mac Fleet has an extremely promising career so we'll have to see what happens with him