Two great guides for any part of the western US would be the "Sibley Guide to Birds" and Peterson's "Western Birds." The Peterson guide might be a little easier to use at first than the Sibley because it prominently shows the field marks that distinguish each species. It's also about 2 pounds lighter than the Sibley's!
However, since you'll be in Monterey where albatrosses, petrels, fulmars, etc., and other normally pelagic birds can be occasionally seen from shore, I would also highly recommend Rich Stallcup's "Birds of the Nearshore Pacific."
You're in for great birding in Monterey! With that deep submarine canyon that runs right up to the beach, they get birds there that you'd otherwise have to go 20+ miles offshore to see. It's one of my favorite places for birding and for whale watching on the entire California coast.
Katy