The entrance is located inside a CAVE (C4 on the map) on the northeast side of this area, below the Sheltered Ridge Base Camp. Approach cautiously.
The snow leopard that lives here will be sitting on a ledge above the cave entrance. If you have the Animal Instincts skill, activating Survival Instinct will help you spot the cat.
I suggest shooting it from a distance with a couple of poison arrows in rapid succession.
Unlike the bear you met earlier, the poison won't slow the leopard down. It will immediately jump down and come at you, but the poison should weaken it, making it a little easier to kill.
As soon as you've shot the two arrows, switch to the rifle and fire quick bursts at the charging cat, backing away as you fire.
Repeat this until it falls. When it's dead, loot the body for exotic hides.
Now you can safely enter the cave. Use a rope arrow to pull off the rope-wrapped barrier over the door at the back of the cave.
Then pry open the metal door, go through...
...and follow the tunnel to the Frozen Gorge Base Camp.