To the north-east of the Somerset Levels, the Mendip Hills are moderately high limestone hills. The central and western Mendip Hills was designated an Area of Outstanding Natural Beauty in 1972 and covers 198 km2 (76 sq mi). The main habitat on these hills is calcareous grassland, with some arable agriculture. To the south-west of the Somerset Levels are the Quantock Hills which was England's first Area of Outstanding Natural Beauty designated in 1956 which is covered in heathland, oak woodlands, ancient parklands with plantations of conifer and covers 99 square kilometres. The Somerset Coalfield is part of a larger coalfield which stretches into Gloucestershire. To the north of the Mendip hills is the Chew Valley and to the south, on the clay substrate, are broad valleys which support dairy farming and drain into the Somerset Levels.