The numerous (200 to over 500) tiny, five lobed disc florets of rudbeckia occidentalis
are yellow when mature, but they soon wither and darken, and the overall color of the flowerhead is purplish-brown, the florets part of on a large cone about 2 inches long (lengthening with maturity), supported by a thick, rigid stalk that may reach a height of 6 feet. Only a small fraction of the florets are yellow at any one time; these move up the cone as the season progresses.
Below the flowerhead is a ring of spreading, triangular, leafy bracts, each over one inch long, while the true leaves, also large, are found at intervals all along the stem. Leaves and bracts are sparsely hairy underneath, and along the edges. The plant is particularly favored by bees, who gather significant amounts of nectar. Most other members of this genus have large yellow ray florets; the Western coneflower is one of the few species where these are absent.