Giant vetch is a large, stout perennial wildflower with succulent stems climbing from 1-2 cm high. The hollow stems are conspicuously ridged (lengthwise) and range from glabrous to pubescent. The leaves are alternately arranged along the stems and are pinnately compound. The 16-30 leaflets are each narrowly oblong to lanceolate in shape and usually 1-3 cm long. The tendrils are found at the tips of the leaves and are well developed. The stipules at the base of the leaves are large and leaflike.
The flowers are in one-sided racemes of 8-16 flowers. The calyx is somewhat villous and about half the length of the corolla. The uppermost pair of calyx teeth are no more than 1 mm long, but the lowest tooth is nearly as long as the calyx tube. The corolla measures 14-18 mm long and ranges from a dull saffron yellow tinged with red , creamy whitish-yellow, or orangish in color. The pods are glabrous and green when young, turning black with age. They measure from 3-5 cm long and 10-15 mm wide.
Giant vetch may be found on moist soils in open forest, thickets, forest clearings and along streams in the lowlands.
Giant vetch may be found along the Pacific coast from Alaska south to California and inland to the Willamette Valley and Columbia River Gorge in Oregon.
In the Columbia River Gorge, it may be found between the elevations of 100'-600' entirely on the Oregon side of the Columbia River from east of the Sandy River east to Angels Rest.