It begins at a spring complex in the Cascade Range on Pumice Flat in the Umpqua National Forest and flows 1.1 miles (1.8 km) north into the North Umpqua in Kelsay Valley, upstream of Lemolo Lake.

Although Spring River and other nearby spring-fed streams are short, their total water contribution to the North Umpqua is significant, especially during dry months.

[3] Thirsty Creek is a perennial stream that flows on the surface upstream of Spring River but sinks underground about 0.5 miles (0.8 km) before reaching it.

The low-flow discharge at the mouth of the river was measured at 210 cubic feet per second (5.9 m3/s) on August 10, 1997, more than Thirsty Creek alone could account for and more than half of the North Umpqua flow above Lemolo Lake.

The river has good spawning gravels, a stable flow, and desirable temperatures for fish.