This happened while I was stationed at an army base in Arizona, as I am still enlisted I will forgo the base and my name. However night while on guard duty, and paired up with another guard we caught sight of a man near the perimeter fence. We yelled for him to stop and show his ID. As we got closer I could see he was a Native American man, standing taller than me, dressed in very old fashioned and kinda steriotypical leather clothing. He had a stoic expression and ran into the desert, leaping down into a nearby trench. It looked like he had jumped over a cliff the way he just went straight down; but we knew that trench wasn't even two feet deep. Running to the trench shouting we are authorized to shoot intruders and to come out quietly all we saw when we reached the trench was a dog or coyote running off into the desert. We searched around the area a little bit but couldn't find any trace of anyone, and trust me when I say there wasn't anywhere nearby to hide, especially not where we wouldn't have seen him in a pretty brightly clear clear desert night under a half moon. We ended up not calling it in or reporting it as at the time the military was pretty quick to dismiss anyone they thought were mentally unsound.