You live near Mills Creek Rd. That would be a great trainging road for Palmsprings. It's posted as a flat century but here is a good climb at the start heading up to 29 Palms. Gets pretty windy in that section too. Don't count on totally flat rides to get you through. Dillon Rd has plenty of roller too. Best to train on gentle climbs for this ride.

Why would you pay to do the River ride 35 miler? Pretty ragged area from what I've heard. If you want to trail ride, try the SART.