My DD8 and I have been to both the San Diego (Chula Vista) and the Palm Springs Soak CIty Parks.
The one in Chula Vista was a lot of fun. We went late June when my DD was six, got there at opening and had short lines for all the various slides. we waited 1 to 10 minutes for the bigger slides, but this was from opeinguntil about 11AM. As the day wore on it got CROWDED with many of the kids tween age and young teens with little to no supervision, so things got a little too rowdy (lots of PDA and foul language) for us, so we went home. It was a long day with only being there for about 5 hours!!
We went to the Palm Springs one last summer some time. Were we nuts? It was so hot, even a water park is miserable. It just was too hot. You got no relief from getting in the water!!
Neither of these are near the amusement park.
So, if you go, go early, take in as little as possible as the lockers for rent are not big, drink plenty of water and leave when the droves begin arriving!! Do slides in the morning, then if staying longer do the wave pool, kiddie area and lazy river later.
Have fun!! AMY