There is only one inhabited home, reached, when the stony track runs out, by pulling on boots and trudging through bogland. John and Michael Gavin's croft stands across a makeshift bridge over a stream, surrounded by lush grass kept at bowling green length by the sheep.
The two elderly brothers have lived here all their lives. Their mother was born here too, in what may be the last croft left after the decimation of the local population by the 1845-49 famine. The Gavins have recently moved into a new bungalow built beside their old croft by the local council, but they still have neither electricity nor telephone. What makes this more poignant, given the elder brother John's fading health, is that the pair are sitting almost literally on a goldmine.
Successive tests since 1987 point to large ore deposits, perhaps 500,000 tonnes, in the area of the valley. Some estimates have suggested that Ir pounds 400m ( pounds 416m) worth of gold is waiting to be extracted. Mining experts say no one will really know for sure until they dig for it.
A Dublin High Court judgment is imminent in a dispute that may decide whether mining can proceed or whether a local council can block government policy. The case has enormous implications for mining projects across a large area of the west of Ireland.
Valuable nuggets were found in earlier times in the valley, washed down, it is claimed, by mountain streams such as the one behind the Gavins' cottage from which the lake is filled. Recent interest has been fuelled by detailed testing and apparently generous royalty policies of the last two Irish governments.
The court row centres on Mayo County Council's decision to block mining in the area to protect its rugged beauty and the related tourism earnings. The ban is effective for the next six years and so far has been rigid, even blocking a project as environmentally innocuous as a talc mine near Westport.
Glencar Exploration, the mining company seeking the court order to overturn the ban, says that in such a sparsely populated area tourism and carefully concealed mining can coexist. Its mine would, it argues, occupy an area of just 1.5 square miles (3.9 square kilometres) and create up to 200 much-needed jobs directly and spin off many more.
John and Michael Gavin seem ambivalent about the gold under their feet. On the one hand all the talk of overnight fortunes excites them. But Doo Lough is the only home they have ever lived in and, newly rehoused, they are not planning on moving.
The Gavins live on the fringe of the likely mining area, where companies may seek agreements for property lease or purchase with local landowners to anticipate possible concerns over disturbance. At this early stage, Glencar declines to specify who this might involve.
The Gavins are therefore still none the wiser about their chances of ever seeing the gold turn into cash in their hands. John, 77, though going a little deaf, is the more talkative. Delighted to see visitors, he comes out eagerly to greet us with his lively two-year-old collie Shap. His talk is of cold winters and getting by against the odds and bafflement at an unseen bureaucracy. 'They said we couldn't have the electricity unless we paid pounds 15,000. And we were supposed to be getting a phone in. We paid half the money - pounds 50 - but we got no reply.'
Glencar, after spending Ir pounds 2m ( pounds 2.08m) on its Mayo exploration, has no plans for a mine entrance within the valley, preferring a forested site it owns to the north-west, where, according to Hugh McCullough, managing director, trees would conceal the workings.
A gravity system where heavier ore particles settle at the bottom might work, but rock structure would ultimately dictate whether a chemical leaching process using cyanide was needed. It is this that alarms environmentalists.
Paddy Hopkins, a local conservationist, argues the Doo Lough water system and inter- linked lakes, fishing, drinking water and all 'could be polluted very easily'. He wants the area from Croagh Patrick to Doo Lough included in a national park, which would sink all mining plans at a stroke. 'Personally I don't think it will ever be mined. The overwhelming majority of people in the area are so opposed they are prepared to go out and physically stop it.'