In old maps, the flat area to the northeast of Achnaha is called Glendrian Moss. It was drained in the eighteenth century on the orders of Estate owner Alexander Murray, Lord Stanhope, as part of his doomed attempts to 'improve' Ardnamurchan by introducing modern agricultural techniques. In the years since, the ditches have silted up so it's probably almost as boggy now as nature originally intended.
I have tried, but this is the first of the day's identification failures. Does anyone know what it is?