I don't remember the KOA as being in Mariposa, but closer in to the park. I don't care for KOA's, but we did a drive thru about a decade ago & it looked pretty good. There is no outstanding FHU facility in the area in my opinion. I recommend the fairgrounds in Mariposa. Was a bit of a challenge to get level and not particularly scenic, but a comparatively easy drive for the RV. And you are definitely going to want to do any driving in the greater Yosemite area in your dinghy. A much prettier location is one of the sites at Lake McClure. There are some 'newer' sites on a plateau overlooking the lake that are beautiful. Water and probably only 30 amp. Sewer dump at the adjacent boat ramp. There are wooded sites in the lower, older campground. I think they are water & electricity. The sites are probably very popular on the weekends.