To the south of Grasmoor is the valley of Rannerdale, which flows to Crummock Water between Lad Hows and the neighbouring Wandope. This drainage is supplemented by Cinderdale Beck, separating Lad Hows from the main body of the fell. The northern flank of the ridge stands above Liza Beck, in the valley of Gasgale Gill. This stream also makes due west for Crummock Water, but is diverted northward by the low top of Lanthwaite Hill to join the Cocker after its exit from the lake. An area of lowland to the north-west is thus annexed to Grasmoor from the natural territory of Whiteside.