It extends northwards from the Bird's Neck Isthmus into Cenderawasih Bay, and is composed administratively of the Rasiei, Wondiboy, Wasior and Teluk Duairi Districts (kecamatan) within the regency.

These densely-forested mountains run north and south along the spine of the peninsula, rising from the shore up to 2,250 metres elevation, and extending southwards into the Bird's Neck Isthmus.

[4] The eastern slope of the mountains is steeper than the western slope, and constitutes a thin coastal strip along the east coast of the peninsula which actually forms Teluk Umar District within Nabire Regency of Central Papua Province.

Lower montane forests are dominated by Castanopsis acuminatissima and species of laurels.

is predominant in upper montane forests, and the trees are often covered in mosses and other epiphytes.