Stems (7-)15-30(-60) cm; base reddish, glabrous to puberulent. Leaves mostly on proximal 1/3 of stem; basal leaves 3-12 at anthesis; cauline leaves 3-5 at anthesis; petiole 2-12 cm. Leaf blade round, 0.8-4 × 1.2-8 cm, ± succulent, nearly glabrous; ultimate lobes 3-15, width 1-8 mm (basal), 1-4 mm (cauline). Inflorescences 3-25-flowered; pedicel (0.6-)1.2-3.2 cm, usually puberulent; bracteoles 4-6 mm from flowers, green, linear, 3-5 mm, puberulent. Flowers: sepals dark blue to white, nearly glabrous, lateral sepals spreading to reflexed, 11-13 × 4-6 mm, spurs straight to gently decurved, within 30° above or below horizontal, 12-16 mm; lower petal blades elevated, exposing stamens, 3-7 mm, clefts 1.5-3 mm; hairs centered, mostly on inner lobes above base of cleft, white. Fruits 14-22 mm, 3.5-4 times longer than wide, puberulent. Seeds unwinged; seed coat cells with surfaces smooth.

Flowering late spring-early summer. Uncommon on moist talus slopes; of conservation concern; 1100-2700 m; Calif.

Delphinium antoninum hybridizes with D . decorum subsp. tracyi and with D . nudicaule . Most often confused with D . decorum subsp. tracyi , it is separable on the basis of its longer root, usually reflexed sepals, and typically colorfast flowers. It also may be confused with D . andersonii ; see discussion under that species.