Redhill is located within the Weald Basin, and the Weald-Artois Anticline. The town is situated in the east-west lying Vale of Holmesdale at a place where there is a natural water-cut gap in the Greensand Ridge, which connects the town with the low-lying land of the Low Weald to the south. Today the Redhill Brook runs through the gap in the Greensand Ridge on its way to join the Salfords Stream and the River Mole to the south. (The brook is now mainly culverted through the town centre: it enters a culvert behind Redhill station and briefly reappears in town at the Halford's car park, before emerging as a free-running stream again in Earlswood). The gap through the Greensand Ridge provides a way south for the London to Brighton railway and the A23 road. The housing of the town is built in the Vale of Holmesdale, and on the hillsides of the two ends of the Greensand Ridge (Redstone Hill and the hillside of Redhill Common), and on the flat of the water-cut gap in between.