Lotus oblongifolius is a species of legume known by the common name streambank bird's-foot trefoil. It is native to western North America from Oregon to northern Mexico, where it grows in moist to wet areas in several types of habitat. It is a spreading or upright perennial herb lined with leaves each made up of elongated oval leaflets each up to 2.5 centimeters long. The flower cluster bears several yellow and white flowers between 1 and 2 centimeters long. The fruit is very elongated, reaching up to 5 centimeters in length but just a few millimeters in width. One variety of this species, var. cupreus, the copper-flowered bird's-foot trefoil, is endemic to the Sierra Nevada slopes of Tulare County, California.