The exact coordinates for the base camp are UTM 53N 712419 3416034.
Lara comes to the Forest Ruins location in the Keep Moving Forward and Gated sections of the game. She gets here after leaving the Sheltered Ridge base camp for the second time and leaves it when Lara and Dr. Whitman open the gate and step through.
This location is mainly an opportunity for Lara to find salvage and learn how to upgrade her weapons and tools. There are a lot of wolves around that will attack her. She will have to use the bow quite often to get rid of them, and learns how to shake them off and kill them with an arrow through the throat in close combat if she didn't shoot them fast enough.