[4] The Calapooia flows generally northwest from its source in the Cascade Range near Tidbits Mountain.

The city of Tangent is also near the river on a branch of one of its downstream tributaries, Lake Creek.

The confluence of the two rivers is about 120 miles (190 km) by water from where the Willamette joins the Columbia River[5] The Calapooia was named for the Kalapuya (also spelled Calapooia), a tribe of Native Americans.

Further downstream are Biggs, Fox, Sweet Honey, Cedar, Pugh, Sawyer, Johnson, and Brush creeks.

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