Arising southeast of Hickman Butte in the Mount Hood National Forest, the river flows northwest between North Mountain on the left and Goodfellow Lakes on the right.

[3][1][4] Most of the course of the river lies within the BRWMU,[7] a federally protected area of 143 square miles (370 km2) surrounding the main drinking water supply for Portland.

[8] Access to the BRWMU is generally limited to government employees and guests on official business, and security guards keep watch on its three gated entrances.

Water was then diverted from the Little Sandy River to Roslyn Lake through a wood box flume.

The decommissioning restored the Little Sandy River to steelhead and salmon runs for the first time in nearly a century.