Leaves, stems and calyx of astragalus hallii
have a light hair covering, less than some similar species. The plant is quite small but branches freely, forming compact mats, and the lower portion of the stems becomes woody with age. Leaves are pinnately compound, the leaflets alternately arranged, and relatively short, around 4 inches. The calyx tube is colored reddish purple, while the five-lobed flower is purple, lavender or blue, with white patches. The two wing petals are relatively narrow, oblong in shape, while the banner is broad, bent back by nearly 90 degrees.