I used to live there, all of the lakes are small. That'll be right in the middle of the spawn. If you like sight fishing, some of the smallest reservoirs in SD like Dixon, Poway, Murray and Miramar have gin clear water and big bass on beds. If you like more "traditional" fishing, El Capitan, Lower Otay, Hodges should be good. There's a website in San Diego called sdfish.com that has info on all of the lakes, and has fish reports published weekly so you can get up to date info on where you may want to focus.
Not all of the lakes rent boats, so check into that before you go too. Dixon, Poway, Jennings, El Capitan (on the weekends), Wohlford do though (there may be more).
