It drains part of the Northern Oregon Coast Range northwest of Portland, originating on the east side of the mountains and flowing in a loop around the north end of the range near the mouth of the Columbia River.

Its watershed of 855 square miles (2,210 km2) includes an important timber-producing region of Oregon that was the site of the Tillamook Burn.

In its upper reaches it flows through a long narrow valley of small mountain communities but is unpopulated along most of its lower reaches inland from the coast.

It receives the Salmonberry River from the east in northern Tillamook County.

[6] Nehalem is also used as the codename for Intel's first-generation line of Core processors.