The headwaters of the River Esk and the Duddon are separated by a ridge falling south west from the summit of Crinkle Crags. This line of high ground continues over many twists and turns for , finally meeting the sea on the slopes of Black Combe. From Crinkle Crags the first fell on this ridge is Hard Knott, followed by Harter Fell and Green Crag. Alfred Wainwright did not include the remainder of the ridge in his influential ‘'Pictorial Guide to the Lakeland Fells'', but later guidebook writers have disagreed, adding Great Worm Crag, Yoadcastle, Whitfell, Buck Barrow, Black Combe and the low hills around Devoke Water to their main volumes. Wainwright himself later relented and included these lesser hills in a supplementary volume, The Outlying Fells of Lakeland.