The highest point in Hampshire is Pilot Hill at , in the northwest corner of the county, bordering Berkshire, and there are some 20 other hills exceeding . Butser Hill, at , where the A3 crosses the South Downs, is probably the best known. In the north and centre of the county the substrate is the rocks of the Chalk Group, which form the Hampshire Downs and the South Downs. These are high hills with steep slopes where they border the clays to the south. The hills dip steeply forming a scarp onto the Thames valley to the north, and dip gently to the south. The highest village in Hampshire at about above sea level is Ashmansworth, located between Andover and Newbury.