The north west boundary of the hills runs up the Crawick Water in a north easterly direction from where the Crawick Water runs into the River Nith. This boundary follows the B740 road through Crawfordjohn and connects to the old trunk road north which was used before the M74 was built on its present route. North of the B740 the hills gradually drop out into the Central Lowlands of Scotland though Tinto is an outlier 11 kilometres north of Abington. The south east boundary of the hills is formed by the Forest of Ae which is one of the largest forests in Britain at 10,000 hectares. A continuous band of trees runs, again in a north easterly direction, from Auldgirth on the River Nith (9 kilometres south of Thornhill), for some 26 kilometres till it meets the M74 motorway 10 kilometres north of Beattock. Continuing south of Ae leads into the plain that surrounds the town of Dumfries.