The A839 is one of the shorter A83x roads, running for less than 25 miles through south Sutherland.
The route begins just north of The Mound, at a T-junction with the A9, in a shallow cutting near sea level, and runs along the hill foot at the north edge of Strath Fleet. Level and lined by birch trees at first, it reaches open land – arable on the valley floor but withsteep crags above – and then rises gently to the village of Rogart.
Beyond Rogart the scenery becomes more varied: still arable land in places but elsewhere there are boulder-strewn and bracken-covered hillsides and patches of trees. The valley narrows, and three miles after Rogart there is almost no level land, but it soon opens out again a little. Beyond Acheilidh the farmland finally disappears and we run through open moor to the summit at about 150 m above sea level.
As soon as we start downhill there are fields and farmhouses again, and after a mile we run along the edge of a conifer plantation before entering Lairg, the main village of central Sutherland. The A839 forms the village's Main Street and runs to a T-junction with the A836 at the lochside. The loch here is a stretch of the River Shin which has been dammed for hydro-electricity, and makes for a pleasant scene.
We multiplex with the A836 south along the shore for about 0.3 miles; the A839 then resumes at another T-junction and crosses the loch – which by now is almost down to river width – on a concrete bridge. It turns left past a petrol station and some houses to leave the village, and soon turns away from the Shin to climb once again. At this point it becomes single track with passing places, having been double track all the way from The Mound.
The road now passes through rough pasture, with a fine view of Ben Klibreck if you look north, and more forestry plantations. There are occasional glimpses of the mountains of Assynt ahead in the distance. We reach a height of 186 m before dropping, still through forest, to meet the A837 at Rosehall.
Originally, the A839 ran westward from the Mound only as far as Lairg; the road beyond there to Rosehall was the B869. However, this situation did not last long and the A839 was extended west in the late 1920s.