The 1920-1922 Central New Guinea Expedition had as goal to reach the mountain from the north coast over a route partially explored in a 1914 military expedition. On February 7, 1920 the first exploration, under leadership of A.J.A. van Overeem started at the mouth of the Mamberamo and followed the Idenburg River. In October, they had climbed across the Doorman Mtns and reached the upper "Swart Valley" (now Toli Valley). Here they made first contact with the Lani people (a.k.a. the Western Dani people), an agricultural people with whom they stayed for six weeks. Running out of time and food provisions, this expedition returned without climbing Wilhelmina.