Stopped on a Sunday evening during a westbound cross country journey. Our 20’ van had no issues circling the road to find an open First-come-first-served spot, but would advise not much longer of a rig. We had to figure out the rules for finding and paying for an open spot, but it was all fine. This is a popular campground with many sites reserved far in advance, so last-minute FCFS openings on weekends may be rare.
Although it is not immediately evident at the entrance, there are two camping areas here. One circle of 8 or 9(?) sites which surround a little pond nearer to the highway, and then second set of 5 or 6 campsites perhaps a half-mile away past an open gate. I was travelling solo, just had a tent. I approached Great Basin Park too close to sunset to arrange for tent camping, so this area popped up along my route. I am so glad i stopped to check it out. I found a spot before sunset, up in the "equestrian' area. Other spots were occupied by some RV'ers but they were very nice. The vault toilets are maintained. The sites are not large but are well laid out and spaced apart, consisting of a fire ring, a grill, and a crushed-rock level area. After dark I had excellent view of the starry skies. Quiet neighbor campers. Seemed safe.