My personal choices would be either Santa Cruz or Petaluma for the same reasons sf7307 cited. Sacramento would be my last choice.

Never been to CA and only 5 - 6 days....why on earth has nobody suggested San Francisco??? March and April are too early to enjoy Ocean swimming even in San Diego (save that for the summer time). SLO??? Come on folks? This is way down on the list of California must sees. Yes the Monterrey - Carmel - Big Sur - Santa Cruz thing is nice too.

But for first-timers to CA, I vote for basing yourself in San Francisco without a car. Then rent a car for one day to go up to Petaluma for the concert, stopping for lunch in Sausalito. Then ditch the car back in SF since parking there is outrageous.

Enjoy.

"Oh - I got it Peace. Are you saying you have not been south of LA?"

Aaaarrrgh. Of course I have. "San Juan Capistrano is the only place I know ON YOUR LIST that's south of L.A". Emphasizing the key words, "on your list".