Perennials, 40–100 cm (caudices unknown). Herbage unevenly floccose-lanate or tomentose, glabrescent. Stems single. Leaves progressively reduced distally; petiolate; blades elliptic-ovate to lanceolate, 10–20(–30?) × 3–7+ cm, bases tapered, margins dentate to denticulate (teeth cartilaginous; mid leaves similar, sessile, smaller; distal leaves bractlike). Heads 10–20+ in loose or congested, cymiform arrays. Calyculi of 5–8+ lance-linear to filiform bractlets (lengths ¹ / 3 – ⁷ / 8 phyllaries). Phyllaries ± 21, 7–8 mm, tips greenish. Ray florets 0. Cypselae glabrous. 2n = 40.

Flowering spring. Steep, rocky slopes; of conservation concern; 400–1500 m; Calif.

Senecio astephanus is collected infrequently.