Between Redhill and Ash the line runs roughly parallel with the North Downs. Between Reigate and Gomshall the line runs along the foot of the North Downs escarpment in the Vale of Holmesdale. At Guildford it passes through the gap in the Downs formed by the River Wey, with two short tunnels just south of Guildford station, and further west between Guildford and Ash the line runs to the north of the Hog's Back. It then follows the Blackwater valley as far as Sandhurst, before continuing to Reading.