Blackdown Hills, range of hills straddling the boundary between the counties of Somerset and Devon, Eng., to the south of the town of Taunton and to the north of the town of Honiton. The hills are developed upon chalk and greensand and are drained mainly by the Rivers Culm (a tributary of the Exe) and Otter. Farming, especially dairying, is important on the chalky soils of the area.