Subshrubs or shrubs, (20–)40–150 cm (taproots woody). Herbage sparsely hairy, unevenly glabrate (usually with persistent tomentum in leaf axils and on abaxial leaf faces). Stems usually multiple (arching upwards). Leaves evenly dis­tributed (proximal withering before flowering); sessile or obscurely petiolate; blades ± oblong or elliptic, (4–)6–10(–12) × 1.5–3 cm (1–2-pinnatifid, lobes ± linear, 1–2 mm wide), bases ± linear, ultimate margins entire. Heads 4–12 in cymiform arrays (involucres campanulate, 8–15 mm diam.). Calyculi 0 or of 1–3+ (inconspicuous) bractlets. Phyllaries (± 13) ± 21, (5–)6–8 mm, tips minutely black. Ray florets ± 13; corolla laminae 8–10 mm. Cypselae hairy. 2n = 40.

Flowering spring. Ocean bluffs, open hillsides; of conservation concern; 0–500 m; Calif.; Mexico (Baja California).

Senecio lyonii is known from the Channel Islands (off the coast of southern California) and south.