Grand Canyon or Yellowstone for 2015?

A recommendation for Southern California is Pechanga RV Resort in Temecula, CA. Wife and I stayed there for Spring Break. It's located roughly half way between San Diego and LA, and has easy freeway access to both. It's a great little park, well laid out and well maintained. It's also connected to the Pechanga Indian Casino, if you are interested in that sort of thing. They are a Reserve America park, so you can get some very good discounts there. Towing through Cali is 55 MPH, so be sure to plan on some extra time. En route from GC to Cali, a nice little campground on the way is Willow Beach, located not far from Hoover Dam on the Arizona side of the border. Full hookups, but be warned: like all of AZ and NV in summer, it's going to be HOT! (This assumes, of course, that you'll swing through Las Vegas on the way). If you're going straight through on 40, there are plenty of campgrounds in Lake Havasu, CA. Needles, CA (the inspiration for "Radiator Springs" in the Disney movie "Cars") has Pirate Cove, located on the Colorado River right at the AZ line.