Ayala made GN Finals this year (12th), and Vista Murrieta did well in their regional BOA trip to the San Antonio Super Regional (20th).
Ayala ( in Chino Hills), Vista Murrieta, Upland, Mission Viejo, Trabuco Hills, Fountain Valley, Cerritos, Los Alamitos, Mission Viejo, El Toro, Chino Hills, Rancho Verde, Rowland High, Arcadia, Etiwanda, Chino, Hart, Thousand Oaks, and quite a lot of bands in the San Diego area are good as well ( San Bernardo, Mt. Carmel). Southern California has one of the stronger group of bands in the WHOLE country, participating in several different local circuits. They regularly do very well against schools from different states and regions in the state. They may not all do BOA, but there are a lot of strong band programs in this VERY large and very populous area.
Texas, Oklahoma, and Indiana schools seem to do the best schools, especially in regards to BOA. California, Florida, Illinois, Michigan, the Carolinas, Penn, Tenn, KY, and Ohio are a step behind at BOA.
California schools have the whole parade scene and bowl scene... So many of them put a lot of rehearsal time into that. Band programs can be strong with doing well at BOA marching band contests.
Concert season, and percussion season, which California percussion sections rule the roost show off the strong SoCal band programs as well.