After leaving Zion NP, I took a detour to drive by the Hurricane Mesa Test Facility. This is the only privately owned and operated supersonic test track in the US and it sits atop the mesa a few miles to the west of Zion NP. Formerly a USAF facility used to develop ejection seats for supersonic fighters (among other things undoubtedly). It's now operated by a subsidiary of Goodrich. Here's their official web site. This site by Paul Freeman has a lot of interesting information about the place along with photos of the aircraft cockpits used. The Wikipedia page for the site is unimpressive. Here's a Google Map of the facility. The Center for Land Use Interpretation has a couple pages on the facility: short description page; newsletter story about the facility. Finally, I found this story from the local newspaper about the facility giving some interesting details about the rocket sled test operations.
I turned onto Mesa Road a few miles west of Zion and stopped to take in the view looking up at the mesa. The first photo shows that view. I spotted a group of people running up the road with a large van following them. Knowing it was a narrow road, I decided to not follow them and interfere with their training / masochism / punishment. Instead, I drove a bit east and turned up Kolob Reservoir Road toward the upper section of Zion NP hoping to drive along Smith Mesa Road and loop back around to the Hurricane Test Facility. I was pleasantly rewarded with a beautiful drive across the scenic mesa tops. There were quite a few ranches and farms up there, and so the dirt road was well worn and easy to drive. It's probably a lot worse when the ground is wet, so I wouldn't recommend it during or after rain showers unless you had 4WD.
When I arrived at the tall chain link fence perimeter of the test track facility, I was surprised to encounter a group of high school aged girls resting and gasping for breath. These were the leaders of that pack of runners that I saw starting at the bottom of Mesa Road. The road skirted the facility and led me to the very steep hill down Mesa Road. At the top of the hill I stopped at a pullout to let the remaining runners and their escort van pass by. Several girls smiled and waved at me as they ran by. They were certainly not in too bad of shape, and that's amazing because I could never run up that hill! The van drove by with a man shouting encouragement from the passenger seat to the final two runners, who were obviously very very tired.
On the way down the road I stopped a few times to take photos. I zoomed in on the trailer that extends out over the cliff's edge. I had read, on one of those sites I linked above, that this trailer is an employee lounge. I'm sure it has a terrific view.