In SoCal there are probably dozens of epic rides to choose from, depending upon what you are looking for.
How about a very large climb?
Up for a challenge? Give this segment a go! Azusa to Dawson Saddle - highest elevation gain climb in continental US (7,152 ft) | Strava Ride Segment in Duarte, CA
Azusa to Dawson Saddle, 7100+ feet of climbing in one segment.
A nice beach century? The old Amtrak Century could fit the bill, Irvine to San Diego with a train ride back.
Or, Santa Barbara to Santa Monica or so.
Around Laguna Beach is the Seven Sisters ride. Something like 35 miles with 6+k? with climbs getting very steep.
Want a gravel race, Belgian Waffle Ride could be pretty epic.
Many options around here.