The valley is drained by the Diveria or Chrummbach, a tributary of the Toce at Crevoladossola.
The highest mountains in the valley are the Weissmies (4,017 m), the Lagginhorn (4,010 m) and the Fletschhorn (3,993 m), all in the Pennine Alps.
The most important pass in the valley is the Simplon, connecting Brig to Domodossola.
The international border runs from the Camoscellahorn to Monte Leone, reaching an altitude of 800 metres at valley floor.
The main localities are Simplon, Gondo (Switzerland), Iselle, Trasquera and Varzo (Italy).