Mendip Hills, range of hills in south-western England; located mostly in the county of Somerset and reaching up to the border of Avon in the north, the Mendips extend about 37 km (23 mi) north-west from the Frome valley. The Western Mendip rises to a plateau over 240 m (787 ft) high, and about 9 km (5.6 mi) wide. The limestone of which the hills consist has encouraged the formation of underground streams and caves, the most famous of these being Cheddar Gorge at the north-western end. Evidence of ancient settlements has been found on the hills, which were later mined by the Romans for lead.