Okay, I ain't your papa, but let me suggest that you first go to (No Longer) Clark Tunnel Road GCGRJT in order to safely turn around and come back down and park at the parking coordinates I've provided. I've added the waypoint and coordinates for this spot. Basically, just continue up Clark Tunnel until you cant go any more. Hey, I'm just thinking about your safety !
You are looking for a small well hidden (well, at least I hope its well hidden!) container. Please replace as found, and most importantly, be safe and have fun!