Really nice basic campground called Rolling M Ranch within Chino Hills SP. We drove up in our 26ft motorhome and while we made it, I’m not sure that I’d want to make that drive again. It’s very narrow and winding, single lane at times, lots of traffic (and so lots of backing up and negotiating around other cars in the narrower sections), and lots of pedestrians/hikers/families walking along the road. It was pretty stressful. 

The campground is nice, free(!) individual unit showers, weak to nonexistent cell service but there’s wifi available through the parks system, I believe it’s free, I can’t vouch for how good it is because I couldn’t get it to work for me from where I was standing. I think it varies and that you have better reception overall in the upper spots. 

Upper spots were not level, but they had a nicer view. Lower spots were more level. Chino Hills State Park is a beautiful place to hike and see wildflowers!