I am trying to make a mountain as my border, so a person could walk up to a mountain and that is what stops them, but they cant walk up it or anything.

I tried using models of rocks and making them bigger but that doesnt work too good and looks dumb. I tried making individual brushes but I cant make it look right.

Is there an easy way to do this?

There are various ways you could probably do this:

1. Create a terrain patch, and use Y to advance edit it. Raise the height a lot, until the angle is steep enough that the player cannot get up there.
   
2. Same as above, but with a shallower angle, then put in a clip brush to prevent the palyer getting any further.
   
3. Use a minefield to sto them going up the mountain?
   

Either way, I'd make the mountain using terrain patches that are massively raised up.

Yeah I was reading through some more posts last night and it seemed that making a terrain mesh would probably be the best way to make a mountain.

Ill give it a try.

Thanks.