[2] The eastern part of the plateau, east of the Sioa River, covers about 525 square miles (1,360 km2) and had a sparse population of 2,100 people (1966 government census), speaking at least five different languages.

Then they camped at the confluence of the Sioa and Rentoul river, in view of three longhouses on the opposite side of the valley, and their inhabitants, who seemed to take no notice of the explorers.

In March 1936, Ivan Champion and Richard Archbold flew over the northern foothills of Mount Bosavi to plan an upcoming expedition from the Bamu River to the Purari.

World War II delayed the planned exploration, and in the meantime a severe measles epidemic greatly reduced native populations, especially of Etoro and Onabasulu people.

That same year, UFM International arrived in the Bosavi area to build an airstrip for a mission station, for which they recruited local workers.