Equine data: terrain limitations, slopes?

It depends on the animal. I've known some horses that won't cross a mud puddle and are terrible on hills no matter how much you work with them.

I've known others that were born for the trail and acclimated to steep, rough and muddy terrain right off the bat.

Some horses conformationally just cannot handle the stress and rigors of rough terrain. Some horses were made for it. Some horses flake out mentally when put in the rough stuff and others really enjoy the challenge.

So the limitations depend on the horse you are riding. I've had horses over the years I wouldn't trust outside of a riding arena and I've had others that I wouldn't think twice about taking down into the Grand Canyon.

Horses are able to go up and down pretty steep slopes. I don't have any specific measurements for you.

When I was a kid I used to ride on the trails and a group of kids had one very steep slope they'd try to take their 4-wheelers and dirt bikes up, most of the time failing. It seemed almost straight up, and was about 50 feet long, I'd guess. I liked to show them all up by taking my horse straight up the trail. I could tell it was a strain, and she was working hard to do it, but she could get up that trail every time, where the dirt bikes failed most of the time.