Even at 60, Richard Long is a towering, physical man. He has trekked across the Sahara, Lapland, and the Himalayas, crossed Ireland in 12 days and lost himself in the Gobi desert and the Norwegian wilderness. For the past 40 years Long has been making journeys and documenting elemental interventions along the way – a line of trampled down grass, say, a cross of raised stones, or a circle of sand.

At times exhaustion and loneliness are implied, as in ‘Sleeping Place Mark’, a flattened patch of grass in a daytime field, or in ‘Reflections in the Little Pigeon River: Great Smokey Mountains Tennessee’, 1970, with Johnny Cash’s lyrics to ‘I Walk the Line’ overlaid, suggesting not only the place and era, but the inner soundtrack of song lyrics going around inside a lonely head.

Long has further emphasised the ‘nature as medium’ message with series’ of drawings on paper, shown alongside gathered or drawn-on objects. Black paper is dipped in river Avon mud, the grey pouring down in visceral gravital drips. Then there are Moroccan tent pegs, children’s Qur’an writing boards and flattened, aged metal scraps from Agadir, all of which are covered in Long’s rather self conscious, giant white thumb print patterns of circles and squares. The site specific ‘Throwing Muddy Water’, is similarly staged, the Firth of Forth mud used to create this work splashed up the wall. Once dried out and cleaned up it seems sterile and ossified, much like the drawn-on objects, and it does seem hard to imagine these gallery works holding much gravitas without Long’s backbone of land art to support them. (Rosie Lesso)

Scottish National Gallery of Modern Art, 624 6200, until 21 October, daily 10am–5pm, £6 (£4).