The Calico campground is in a sloping canyon - nothing to be worried about, but you should bring some leveling blocks in case you need to drive the trailer onto them to level it side to side.
And bring a couple of pieces of wood you can use to chock the tires in case the site slopes front to back. Otherwise, if you unhitch on a slope, the trailer's weight pressing against the hitch jack is all that keeps the trailer from rolling downhill. Before you unhitch, chock the trailer's wheels then put the truck in neutral and release the brakes momentarily to set the trailer tires against the chocks. Then put the truck back into park, apply the parking brake and unhitch.
When you hitch up to leave, just back up a couple of inches to release the pressure on the chocks.
My apologies if you already know this, I just wanted to pass along a couple of tips I learned along the way. <g>
My favorite Calico moment happened many years ago and has nothing to do with the town itself. I stopped there for a couple of nights on my way back from a convention in Las Vegas, and as I was leaving I turned on the radio and heard the first Space Shuttle was getting ready to land at Edwards AFB. The announcer was warning people against trying to get onto the base because traffic was backed up all along Highway 14 into Los Angeles.
I was just approaching the North Entrance to Edwards off of Highway 58, so on the spur of the moment I turned off. There were only a couple of other people going that way, the MPs at the gate waved us through so I followed them to the public viewing area. Once I was there I put out my trailer's awning, set out my lawn chair and had a front row seat in the shade for the landing.