There is an embarrassment of riches there in SoCal for day rides, most of them canyon roads. You can do Mulholland in the Santa Monica mountains (along the coast near Malibu) and check out the world famous Rock Store (a popular weekend hang out, I saw Jay Leno there once on one of his MV Agustas). There's also Glendora Mountain Road to the east, Ortega Highway in OC (runs from San Juan Capistrano to Lake Elsinore), Palms to Pines Highway (Idylwild to Palm Desert; both Ortega and PtP are part of Highway 74), Highways 76, 78 and 79 through southern Riverside County and North San Diego County, which gets you to Palomar Mountain.
For dirt excursions, you could always head over to the San Bernadino mountains; there will be snow, but nothing like Colorado. There are dirt roads that cross the Cajon pass. Also in that area, Highway 173 is paved, but becomes a dirt road and takes you over the mountains to Hesperia, in the high desert.