Head on up to the top of Mount Chiliad using the gondola service. Go over to the right and move along the trail. Look around the edges to find your target, Glenn Scoville. He is about to Base-jump off the mountain, and does when Trevor approaches in order to escape him. There is a parachute by the cable car exit, and a second by the dirtbike. Grab either, and then jump after Glenn. Deploy it and come in for a landing after Glenn. If you're going for a live capture, pull out the Stun Gun and shoot him to bring him down, or just get close to him and Trevor will knock him down. Otherwise, pull out any gun and shoot him.