[4] It drains 766 square miles (1,980 km2) of the Cascade Range on the eastern side of the Willamette Valley east of Salem.

[4] It rises in the high Cascades in eastern Linn county, northwest of Three Fingered Jack in the Willamette National Forest.

It flows north through the mountains past Marion Forks, receiving the drainage from the western slope of Mount Jefferson.

Continuing west, the river flows past Gates, Mill City and Mehama.

Blocked by Big Cliff Dam near Mill City, the lower North Santiam River supports spring chinook salmon and summer steelhead.