The east end of the Moffat Tunnel is a rather fascinating complex. The tracks enter a man-made structure about 500 feet before they actually enter the mountain. This structure at East Portal is where the equipment to ventilate the tunnel is located. Gigantic fans are turned on and suck fresh air in from the west portal and blow out exhaust here at the east portal.
At one point in the past, the fans blew fresh air in from the east portal, blowing the exhaust out the west portal. However, the town of Winter Park was not thrilled with the exhaust being blow out and around the ski resort and town, so the fans were reversed. If you are ever near East Portal when the fans activate, you will definitely hear them.
Also visible in this shot is the Moffat Water Tunnel. A tunnel built parallel to the tracks, which brings water from the west slope to the front range, ultimately winding up in Gross Reservoir.