The spine of the Cotswolds runs southwest to northeast through six counties, particularly Gloucestershire, Oxfordshire, and southern Warwickshire. The northern and western edges of the Cotswolds are marked by steep slopes down to the Severn valley and the Avon. These are a result of the broken edge of the limestone layer. On the eastern boundary is the city of Oxford and on the west is Stroud. To the south towns as Cirencester, Lechlade, Tetbury, Beverston and Fairford mark the southern limit of this region. 