 The Quantock Hills are a 20 kilometres ( 12 mi ) long broad ridge from the coast near Watchet in the north to near Taunton in the south . They reach 384 metres ( 1 @,@ 260 ft ) high at Wills Neck and are separated from Exmoor and the Brendons by a rift valley . The Quantocks and the Brendon Hills at the eastern end of Exmoor are formed by thick sequences of slates and sandstones of Devonian age that were deposited by large deltas that built out into a shallow sea . 
