Castle Rock campground in Fishlake National forest is one of two campgrounds that serve Utah's Fremont Indian State Park, with both administration and reservations handled through the Utah State Park system. When I visited it was both very clean and very well maintained. Despite being close to the interstate, it is far enough up a side canyon that you do not hear the traffic on the road. It feels like being much further from civilization.
There are 44 camp sites available, many alongside the creek that flows through the campground. About 2/3 are reservable, the rest are available daily as FCFS. Two have teepees for those lacking a tent. Several are double sites for larger groups, and there are a variety of pull through vs in/out options.
There is available potable water at several locations around the campground, and two restroom facilities - a full flush unit near the center of the grounds, and a double pit at the south end of the loop.
Every site has a fire pit, an elevated grill, and a picnic table.
There is an access road from the campground to the Paiute ATV trail. For hikers, the south end of the campground is the north origin of the Joe Lott Trail that heads into the Fishlake National Forest. The facilities of Fremont Indian State Park are about 1/2 mile away, on the opposite side of I-70, and include a small museum of Fremont life, and a variety of improved and unimproved trails leading to many rock art sites.