It's in northeast frontier near homestead. I think it's in the chapter 6, final session if u want to try.

You have to go to the Diamond Basin Peak. It's also where you have to do one of the Boston Brawler missions to fight the indian guy.

Head to your hometown in the North of the frontier, head South towards Diamond Basin via the road. at some point you'll have a fork in the road, hang left. On your right there should be a lake with the road going around it. along the road there is a tree which sticks out over a cliff. Dive of the tree, that should do the trick.

You can find this one anytime you're ready:
South of your village, along the path, take the left fork around to the east side of the lake (up into the rocky part).
On the right side about twenty metres from the path is an unusual tree: one trunk has been cut off, another points upwards, the third hangs out over the lake, and is completely bare of leaves. There are some black birds hanging out on the end, which are visible from the path. Run and jump. You'll get the challenge before you even hit the water.