The Bear River originates at Emigrant Gap, as a tiny stream on the border of Nevada and Placer Counties in the Tahoe National Forest. The headwaters are on a ridge immediately to the south of the South Yuba River and north of the North Fork American River. The river flows west into the Bear Valley then enters a deep and narrow gorge, passing the community of Dutch Flat. Continuing along the Nevada-Placer County line it receives Steephollow Creek from the north before widening into Rollins Reservoir, formed by the high Rollins Dam east of Chicago Park. While part of the reservoir, the river is joined by Greenhorn Creek from the north.