Yucaipa, in the San Bernadino Mts, has a population of 51K and an excellent regional park. We stayed here 3 years ago and are delighted to be back. The park has RV and tent camping, trails, water slide, frisbee golf, 3 small lakes stocked with large trout, game fields and more. I rank it one of the top 4 parks we've visited in North America. The other top-ranked parks are one each in MN, NB, OR.
Middle Lake, lots of fishing. Saw a beautiful 8 pound trout caught by a teenage girl who was justifiably proud to show it off.
Upper Lake with woman, dog, rocks, fishermen.
Fantastic weather here, mid 70s for highs, sunny, 40ish for lows.