From its source at the confluence of its east and west forks near Summit, it flows generally southeast from the Central Oregon Coast Range to Corvallis.

[7] The other story is that Wayman St. Clair, who represented Benton County in the territorial legislature in the early 1850s, named the river for Mary Lloyd.

[9] In 1853, the legislature changed the name of the town to Corvallis, a compounding of Latin words meaning heart of the valley.

Turning southeast, the river flows just south of Route 180, receiving Devitt Creek from the left before reaching the unincorporated community of Blodgett.

Here, about 32 miles (51 km) from the mouth, it crosses under U.S. Route 20 and in quick succession receives Norton Creek from the left and the Tumtum River from the right.

About 14.5 miles (23.3 km) from the mouth, it flows under Route 20 for the third time, immediately receives Woods Creek from the right and turns southeast.