The only seen I can remember is that there is a group of kids in there mid 20's and they are hiking out in the forest or something. There is a particular seen where its night and a few people from the group go rock climbing on a cliff near a river and it turns out one of the girls pushed another off the cliff and killed him/her then she/he goes on to kill the rest of the group one by one.

If you can think of this movie, please let me know the title.

It sounds like one of the Sleepaway Camp movies.