Welcome aboard, not only to camping but to a great forum to share all things camping!
Have not posted my review yet, but roughly 14 miles east of Temecula, California is: Rancho California RV Resort.
Listed here under Aguanga, California. Located off I-15, then east on south highway 79. Full hook-ups (20, 30, 50 amps) on large concrete lots: some basic, some with lavish outdoor kitchens. Tons of grass between lots. Verizon, Sprint and ATT cel phone and air-cards work. Renting from absentee owners (via the very pleasant HOA team, Fairway Associates) is the best value for longer term stays. Ranges from $400 - $750 a month.
All kinds of walking opportunities, with or without your dog. Need a leash and baggies while in the park, but plenty of great trails outside the gates. Mainly a golf resort set into the back country of southern California. Little (just under 600 sites) oasis of green grass and ponds, surrounded by the San Diego County Palomar mountain range.
You did not elaborate on your rig, so I'll make note that this particular park requires rigs 30 feet or longer; generally not older than 10 years, (some beautiful exceptions here though) and as of this date, will not accept toy-haulers. You will need a tow vehicle to best enjoy the surrounding area.
No ATVs (generally southern californians are desert bound with toy-haulers full of ATVs...thus the sensitivity at this resort.)
Stay for a long weekend, couple months (it's 60-70 degrees here in winter), or for ever.
Not a lot going on if you have small kids to entertain; but if walking a dog, reading a book, birdwatching, photography, golf or just relaxing by the pool sounds good, it's a winner.