Former federal park ranger here. I worked a season in western Colorado in the San Juan Mountains, and had two encounters that scared the shit out of me, ultimately leading to my resignation.
The first one happened during a trail count. Rangers will bury pieces of technology in the ground at trailheads that shoot a thin, invisible laser beam across the trail; when something magnetic, like a boot or a UTV or even a pickup truck, crosses the laser line, then the counter stores the data point. It's a way for rangers to track visitor usage.
On a particularly hot day, I went out into the field with another park ranger to check on the trail counters and download visitor use data. We pulled up to a two-track UTV trail that was tucked away in the thick junipers, and got to work searching for the trail counter.
Our search led us down the road about half a mile, where the trail suddenly turned downwards into a steep decline leading into a low river valley. We could hear intense buzzing as we started to descend, and my colleague stopped in her tracks; she's allergic to bees, so I started looking for the hive in order to ensure that she didn't get too close & accidentally get stung.
The bees weren't bees; they were flies, hundreds of them, and they were swarming something in the middle of the trail. I approached to take a closer look, and the flies dissipated, revealing a thick slab of meat about the size of my palm. It was pink, with human flesh-colored skin, and coarse, black hair stuck out of it. There were more flies; as I started walking, I saw several more similarly-sized meat chunks spread in a straight line down the hill. They were right in the middle of the road, all with that coarse, black hair sticking out of human flesh-colored skin.
My colleague freaked the fuck out, and I called the state department of fish & wildlife as well as our law enforcement ranger to let them know the coordinates of what we'd just found. I took pictures for documentation and headed back up the road with my colleague, all the while attempting to calm her down. We finished our trail count and got the hell out of there. I never heard back about what those chunks of meat were.
The second encounter I had was a little more sinister. Another colleague and I were driving in a UTV up a treacherous mountain ridge, along the side of a plateau that dropped straight down into a river valley thousands of feet below. Not even rocks or trees would stop that fall. We were taking the trail nice and slow, sketched out by the sheer drop-offs on both sides of the road, when we came across a full-size pickup truck at the top of the hill. It was pulled off to the side, resting against the very edge of the cliff that dipped down into the river gorge, and its tires were all flat, windows smashed open, the truck itself rotting in the hot sun. Keep in mind, we'd had enough trouble getting up there in a tiny side-by-side; this was a full-size Ford F-150. We cut the engine of our UTV and tried to assess the pickup for a minute; as soon as the smell of the gas from our UTV dissipated, I was hit by the sweetest, most rotten stench I've ever smelled. It was like something had been baking under the sun for a long, long time, and it was coming from the inside of the truck.
I asked my colleague if he wanted to get closer to investigate, and he responded, "I do not." So, I took pictures, marked the coordinates, and we carried on with our work for the day. As soon as I had service, I sent all of the info along to our law enforcement officer.
Later that night, he texted me back asking for additional information; after I told him everything I knew about the truck's whereabouts, he said, "Great work!", which I took to mean that something was, indeed, very, very, very wrong about that truck.
I never heard back about that one, either.
I was very freaked out at the time, and my season was almost over; the straw that broke the camel's back was when we nearly toppled off a cliff while traversing a UTV trail that surpassed our skill level. After that, I decided my life- and sanity- were worth more than the wages I was earning, and I quit soon after.