Stems 0.5-2 dm, unbranched or branched (several, ascending) near base. Basal leaves soon withered. Cauline leaves: blade somewhat fleshy, narrowly linear, (1-)1.5-3(-4.5) cm × 0.5-1 mm. Fruiting pedicels 2.5-4 mm. Flowers: sepals 2.8-3.2 × 0.5-1 mm; petals 8.5-10 × 2-2.5 mm, margins not crisped, claw attenuate to base, 5-6 mm, longer than blade; filaments: abaxial and lateral pairs distinct, shorter, adaxial pair ± connate, 4.5-5 mm; anthers ca. 0.8 mm. Fruits erect, (1.5-)2-2.5 cm × 0.7-0.9 mm; style (1.5-)3-4.5 mm. Seeds reddish to dark olive-brown, 1-1.3 × 0.5-0.6 mm. 2n = 28.

Flowering Mar-Apr. Patches of open, relatively moist, heavy clay soil dominated by native grasses, geophytes, and annuals; of conservation concern; 700-1100 m; Calif.

Sibaropsis hammittii is known from two areas, separated by about 120 km, in the Peninsular Ranges of southern California: the Santa Ana Mountains in Riverside County, and the Viejas and Poser mountains in San Diego County.