Did Mount Baldy last time, but I know snow can close that road.
How difficult of a ride? Great Western Loop has a bit of climbing or you can ride the north coast from Oceanside to Dana Point.
throw in Elfin forrest / del dios loop if youre going up the 5.
Are you stopping in LA? The best LA rides go North along PCH (Highway 1), and then go up one (or more) of the canyons:
Topango / Old TopangoMalibu CreekLatigo CanyonTrancasEncinal Canyon Rd
Decker Rd
Have a great time
Thanks to all for the suggestions, and have great holidays, too!
Down towards S.D. way you could ride out to and up Palomar. And their is nothing wrong with a few hill repeats up Torrey Pines.
Peter Sagan doing the Swamis ride out of Encinitas on the 5th.
Bonsal, Fallbrook, Palomar for some good climbs. Camp Pendelton (part of Oceanside 70.3 course) for 30 miles (one way from south Gate to San Clemente) of non stop riding (read: no lights, limited traffic…take ID).
Cool in the early AM, need arm and leg warmers. Check TCSD or Nytro sites for group rides.
Enjoy!
Are you stopping in LA? The best LA rides go North along PCH (Highway 1), and then go up one (or more) of the canyons:
Topango / Old TopangoMalibu CreekLatigo CanyonTrancasEncinal Canyon Rd
Decker Rd Have a great time
All the above are good rides. A group of riders generally meets at Ocean Ave. and San Vicente Blvd. (in Santa Monica) every Saturday at 7:30am and heads north up PCH. This is typically filled with tri riders, with some roadies as well. Usually some of the riders will hit at least one of the above climbs.
Down in the South Bay, a group leaves at 8am every Saturday from Starbucks Coffee in Redondo Beach on Avenue I. This is a big group of roadies, though, and they don’t like tri bikes…
instead of driving bike between SD / LA 
.