From Festipedia, hosted by the FR Heritage Group
Pont Cae'r Gors (English: bridge at the swampy ford) or Pont Rhyd y Gors lies almost at the summit of the line, which reaches 650ft (almost 200m) above sea level in the eponymous swamp. There is a small and controversial bridge known as UB125 at this point; the line runs downwards to the north into Pitt's Head Cutting and to the south at 1 in 40 (2.5%) into Cwtting Cae'r Gors, which was dug out of unstable glacial till, presumably in 1922. It is not a favourite structure, as the sides have to be watched in case they collapse. The bed rock below is impossibly hard to cut without serious use of explosives. There is an almost blind bridle crossing near the top end; the forest roadway crossing was moved to the bottom end of the cutting on this account. When the track was laid through here in 2006 the air temperature was 32°C and the rail temperature reached 48°C. The gradient continues down the hill at an unmitigated 1 in 40 for several miles to Beddgelert and can be a tricky place for a locomotive on a damp day - works trains have taken 10 minutes hence to Hafod Ruffydd and taken an hour to get back. Once you have left the cutting, the view south peering into the Aberglaslyn Pass from a height, is superb.
