Nice work! I think you're right. Boomer must be at Roubaix Lake Campground, inbetween Deadwood and Hill City, South Dakota. He was probably tired after walking 245 miles from his home, huh?
Well, let's see if we can guess what he did next. It shouldn't be too hard.
He woke up after sleeping for 14 hours.
He found his way down Loop C towards Roubaix Lake. He probably pooped near the outhouses, knowing Boomer.
He walked over the small bridge and meowed a few times for no apparent reason.
He walked clockwise around the lake, walking SW down the shore (Cats always move in clockwise fashions, have you noticed?)
At the SW end of the lake, he stopped when he came to a swampy, uncrossable area. He was pleased to see cattails growing here.
Boomer watched the fish jumping in the lake, but soon became increasingly tired (he had been awake for almost a half an hour at this point remember), so he looked for a place to sleep.
He looked to his left and found a large dead tree on the ground, it's tip pointed uphill. Using the downed tree as a guide he took 97 cat steps (42 human steps) from it's tip uphill.
He found another downed tree at this location. The tree was broken near the ground, creating a jagged hollow in the broken trunk. Here, near the ground, under a few pieces of bark, Boomer took a nap.
He's probably still there sleeping. Until he gets hungry, anyway.
Maybe you could stop by and wake him up and tell him he better get home soon?