This is the largest of Berkshire's BOAs with a total area of 4494ha.

The extensive area encompassing the many woodlands on the clay and Head topped chalk from Aldworth and Basildon in the north to the edge of the Pang Valley in the South. The boundary with the adjacent Blewbury to Streatley Downs is largely dictated by the areas with more extensive, steeper chalk which are included in that area instead.

Joint Character Area: Thames Basin Heaths. The escarpment along the Thames is part of The Chilterns and small areas are with the Berkshire and Marlborough Downs.

Geology: Much of the area is covered with Head and Clay-with-flints. In places, especially where valleys cut through the area, there are areas of chalk. In the south, especially south of the M4, Reading Beds (Lambeth Group) is the main underlying geology with River Terrace sand and gravel and London Clay clay, silt and sand on the top of the hills in the area, such as Burnt Hill.

Topography: A gently rolling plateau cut through by chalk valleys, along with an escapement along the eastern edge. The southern area slopes down to the Pang Valley and the area is rather more hill like in nature.

Biodiversity:

• Lowland Mixed Deciduous Woodland – numerous woodlands, many are ancient woodland and there are some extensive areas.
• Parkland: Large National Trust site at Basildon Park. 

Access: Basildon Park, Ashampstead Common, Frilsham Common and Burnthill Common. Numerous bridleways and footpaths including old green lanes such as Pinfold Lane while tracks at Frilsham are part of a defined Berkshire Circular Route.

Targets and opportunities: woodland management, chalk grassland re-creation especially on the valley that runs from Bradfield to Aldworth. The Pang, Kennet and Lambourn Valley’s Countryside Project works within this area and there are good landowner relations.