Perennials; (caudex woody, often elevated); (glaucous), glabrous, (petioles and sepal apices pubescent). Stems unbranched or branched (few), 2.5-8.6 dm. Basal leaves not rosulate; petiolate (petioles ciliate); blade oblanceolate to spatulate, 2-8 cm (7--25 mm wide), margins remotely dentate apically. Cauline leaves: blade ovate to lanceolate, 2-10 cm × 5-28 mm (smaller distally), base amplexicaul, margins entire, (apex acute to acuminate). Racemes ebracteate, (lax in bud). Fruiting pedicels divaricate-ascending, (straight), 4-7.5 mm. Flowers: calyx campanulate; sepals (ascending), pale yellow to white, (broadly oblong to ovate) 5-9 mm, not keeled; petals white, 7-11 mm, blade 2-4 × 1-1.3 mm, margins not crisped, claw 6-9 mm, wider than blade; stamens nearly tetradynamous; filaments: median pairs (distinct), 6.5-8.5 mm, lateral pair 4.5-5.5 mm; anthers (all) fertile, 3.5-4.5 mm; gynophore 0.5-1.5 mm. Fruits ascending to spreading, smooth, straight or curved, flattened, 5-12.7 cm × 1.5-3 mm; valves each with obscure midvein (at least distally); replum straight; ovules 36-56 per ovary; style 0.8-2.5 mm; stigma subentire. Seeds oblong, 2-3 × 1.4-2 mm; wing 0.1-0.2 mm wide at apex. 2n = 28. Flowering Jun-Aug. Dry open pine or cypress woods, chaparral; 1200-2500 m; Calif.; Mexico (Baja California). Streptanthus bernardinus is known from San Bernardino and San Diego counties; in Baja California it is restricted to Sierra Juárez and Sierra San Pedro Mártir.
The chromosome number 2n = 14, reported by R. C. Rollins (1993) and by R. E. Buck et al. (1993), must be an error for n = 14. No other species of Streptanthus or its immediate generic relatives has such a low number.