Peter Jennings is correct about the Yuma Arizona location. Most of the information at the Wiki link is "more modern" than when I was there, but the demographic data doesn't appear to have changed much.

I was at Yuma Proving Ground for about a year and a half, ca. 1964 - 5.

For the curious, the main truck I was assigned to wear out was one of three prototypes (Chrysler) of the XM410E1 (1) or XM410E1 (2)2. The second image might be taken at YPG. The driver resembles one of the mechanics there at the time, but isn't our principal test driver(?) for that vehicle. Fort Knox (Kentucky) also had one in testing at the same time and their test course included similar "roads"(?).

The Marines sank their proptotype about 60 ft deep in San Diego Bay during a "swimming test" about midway through their test (unkonwn whether it was ever recovered). The guys at Ft Knox got theirs stuck in a mud puddle for about 3 weeks at about the same time, and a tree stump removed one of the 8 axles on mine at Flagstaff Ordnance Depot during "high altitude operations." A very comfortable ride on rough terrain, but not very tough or maintainable.

The XM410E1 (2.5 Ton Chrysler) never made it past the prototype tests, but the XM656 Ford 5 Ton that one of the feather merchants was testing at the same time (also at YPG) got limited deployment.

About midway through my tour at YPG during the winter when it got hard to depend on getting the 105F (47C) minimum air temperatures needed for "desert environmental testing" about half of the military personnel were shipped to Greeley Alaska for "winter arctic tests" and went from 105F (47C) to -60F (-58C) for a couple of months. I didn't get to go because of the five vehicles I had in long term (endurance) tests that needed to be kept running.

John