The northern boundary of the fell is formed by the walkers pass from Longsleddale to Mosedale, which crosses a marshy depression at 1,555 ft. Mosedale beck has its source here, beginning its long journey north east to Swindale. Beyond the depression the ground rises again northward up Selside Brow to Branstree, the highest Lakeland top east of Longsleddale. South of Tarn Crag is another boggy col, separating the fell from its near twin, Grey Crag. This holds the diminutive Greycrag Tarn, actually a series of small pools on the bed of a larger body of water. The tarn empties into Longsleddale via Galeforth Gill, but issuing eastwards from the same marsh is Little Mosedale Beck.