I was there the same weekend as the horse event, and the red and green trails were trashed, just as Green Giant says, and the above pictures show. The green loop especially took it bad, and I decided not to do my usual second lap because the riding was so miserable. You couldn't escape the piles of horse crap, and the trail surface was so churned up it just wasn't enjoyable. They even rode thru Granny's - I don't know WTF they were thinking. There were some harsh words between bikers and equestrians on the trail and in the trailhead parking area that Sunday for sure. From what I experienced that day, I thought the trails were toast, and that we had lost the magic that is Fort Custer for an unforeseeable time.
Fast forward to last weekend, and it was a rain-out here in Oakland County so I went southwest in search of dry trails. Saturday I hit T K Lawless (BLAST!), then Sunday I headed for home by way of Fort Custer. I almost didn't go, for fear of what I may find. If it looked bad, I was just going to continue on to Yankee Springs. To be honest, I was very surprised at how well the trails had recovered after just a couple of weeks and some hard rain. It was apparent that someone had also been out working on some of the usual trouble spots too, so I'm sure that helped. Most of the cratered trail surface on Green had settled, and there was not much horse *beep* on either trail. The cynical side of me had me believing that the horsey people may not be tough enough for the cooler fall weather, and that may explain why the trail was left alone to recover. But no matter, the trail was much better.
For sure, there are still areas that could use some work, and the one uphill RH switchback shown in the last picture needs some fill, or a reroute because of the deep, loose sand and roots. That was the only spot I couldn't clear on either lap, having to dab, and restart. But overall, Custer was back to fun last weekend. In fact, I was thinking about this thread when I was riding, and I wanted to add an update when I got home, but decided to leave it alone for the time being. I didn't want to downplay the damage done, and was concerned that any positive comments could undermine the goal of getting Equestrians off the multi-use trails. I'm convinced that's what needs to be done for everyone's health, safety, and enjoyment, and the sooner, the better. But for now, get out and ride Custer. It's still one of the funnest trails in Michigan.