So I'll start by saying these are all "wild" trails that we're currently in the process of getting made official - it's been a long, long journey and I've been working with landowners now for the better part of 7 years.
There's one trail that's basically just 22 berms going down the hill - it's steep and loose with well shaped berms.
I went to go up and do some work on it yesterday only to find that some kids have taken out some of the corners, added a couple of jumps using the existing trail as a dig pit, and have straight lined the end to fire directly onto the fireroad. About 1/4 the track is basically completely changed from what it was.
It's literally like they'd seen the trail and decided it's easier put another, completely different trail right over the top of it than to dig somewhere else. The existing trail has been there 10+ years and has been regularly maintained and is ridden daily.
I found the kids digging it and have had a word with a plan to get them involved with the regular crew.
But what the hell! I've never known anything like it.