Plants perennial, bushlike, with subterranean caudices. Stems multiple, erect or decumbent, straight; branches along entire stem, distal longest, antrorse, upcurved; hairy. Leaves: blade 18.8–62.7 × 11–36 mm, widest intersinus distance 8.9–28.8 mm; proximal broadly elliptic to obovate, margins dentate to serrate, teeth 8–12, slightly antrorse or perpendicular to leaf axis, 1–4 × 1.7–6 mm; distal ovate or obovate, base not clasping, margins dentate to serrate, teeth 6–12, slightly antrorse or perpendicular to leaf axis, 1–3.5 mm; abaxial surface with complex grappling-hook trichomes, adaxial surface with needlelike trichomes. Bracts: margins entire. Flowers: petals golden yellow, 6.7–9.5(–12.6) × 2.3–5.8 mm, apex rounded, glabrous abaxially; stamens golden yellow, 5 outermost petaloid, filaments narrowly spatulate, slightly clawed, 5.4–9.2(–11) × 1.3–2.7 mm, with anthers, second whorl with anthers; anthers twisted after dehiscence, epidermis smooth; styles 4.1–6.8(–9) mm. Capsules cup-shaped, 5–9.8 × 5–8 mm, base rounded, not longitudinally ridged. Seeds: coat anticlinal cell walls straight, papillae 3–5 per cell. 2n = 20, 22.
Phenology: Flowering Feb–Oct.
Habitat: Bases of steep cliffs in crevices composed of basalt, granite, and limestone, steep gravelly and sandy slopes, sandy washes.
Elevation: 90–2200 m.
Ariz., Calif., Nev., Mexico (Baja California, Sonora).
Populations of Mentzelia puberula are associated with the Colorado River in Arizona, California, Nevada, and northern Mexico. Disjunct populations also occur in the Gila Mountains of Arizona.