Try driving in your state on CA395 for cool temps. Otherwise, the coast or get into other states. Like someone mentioned, you are probably not going to find a park similar to a winter snowbirding park with lots of activities and like-minded folks. Summer is for families. Fun Valley RV in South Fork, CO is definitely a family place with lots of kiddie activities.
In summer we sometimes went to Escapees RV Club's park in Chimacum, WA on the Olympic Peninsula. Otherwise we were in national forest campgrounds or boondocking on national forest or BLM lands. It's easy to find 'cool' places. We didn't need planned activities. We did 4-wheeling or hiked.