Were the guys driving trucks or cars? If they were driving trucks, then they were probably out in the desert to check on their cows that would be ranging in that area this time of year. One of them could have been my dad. If they were cars, then it was probably drugs.
I know exactly where that fire hydrant is. A couple families who range their cows out that way use the fire hydrant to fill up a 4500-gallon water tanker truck. They park the water tanker truck next to a water trough in the desert. They set the water to drip out of the tanker truck just enough to keep the water trough full. I am not entirely sure how they were able to get the fire hydrant out there in the first place.
As far as the mounds, I know that either the Utah Historical Society or some of the families did a restoration of the cemetery and put up additional fencing. They may have rebuilt some of the mounds at that point, but am I not entirely sure.