Plants 15-45 cm. Cauline leaves: largest proximal to mid stems; blades sometimes ± 3-nerved, oblong or elliptic to broadly-oblanceolate, 10-15 cm, faces sparsely hirsute (mostly abaxially and near margins). Heads borne singly, erect. Involucres hemispheric, 25-40 mm diam. Phyllaries (usually outer 3-4+ foliaceous, 3-10 cm, curling over heads) lanceolate to lance-oblong (margins usually ciliate, abaxial faces densely pubescent or glabrate). Paleae chartaceous, relatively firm. Ray florets 12-21; laminae (10-)20-30 mm. Disc corollas yellow. Cypselae weakly compressed (plump in middles, edges thin, faces, glabrous); pappi 0 or of 2 ± subulate scales. 2n = 30.

Flowering Apr-May. Grassy hillsides; 0-1200 m; Calif.

Helianthella castanea is known only from the San Francisco Bay area.