Annuals; sparsely to densely hispid or subglabrate. Stems erect or ascending, unbranched or branched distally, (hollow, sometimes slightly inflated), 2-12 dm. Basal leaves rosulate; petiole 0.5-3.5 cm; blade oblanceolate to oblong (in outline), 1.5-11.5 cm × 5-55 mm, margins pinnately lobed (lobes dentate). Cauline leaves (distalmost) sessile; blade lanceolate-linear, margins entire, (surfaces sparsely hispid). Racemes (somewhat lax), without a terminal cluster of sterile flowers. Fruiting pedicels ascending, 9-25 mm, hispid or subglabrate. Flowers: sepals erect, (creamy white), lanceolate to ovate, 3-6.5 × 1.8-2.5 mm (equal); petals creamy white, 6-10.5 mm, blade 3-4 × 1.5-2 mm, not crisped, claw narrowly oblanceolate or oblong, 3-6 × 2-3 mm; filaments in 3 unequal pairs, abaxial pair 2.5-6 mm, lateral pair 1.5-4.5, adaxial pair 4.5-8 mm; anthers narrowly oblong, unequal, 2-3 mm (adaxial pair slightly smaller). Fruits divaricate to ascending (sometimes curved), terete, 6.5-12.5 cm × 1.8-2.2 mm; valves each with prominent midvein; ovules 78-96 per ovary; style to 2 mm; stigma slightly 2-lobed. Seeds 1-1.6 × 0.7-1 mm.

Flowering Mar-May. Rocky areas, chaparral, scrub; of conservation concern; 150-1800 m; Calif.

Caulanthus hallii is known from Riverside and San Diego counties.