Plants 1-10 m; young thorns densely puberulent; mature thorns 33-82 mm, 1.2-2 mm at base (20+ times longer than base width). Flowers: petals 4-4.8 mm; style 1-1.2 mm, straight (sometimes uncinate or S-shaped when dry); gynophore (stipe) 0.5-0.8 mm. Flowering Mar-Jul. Desert areas; 0-900 m; Ariz., Calif.; Mexico (Baja California, Baja California Sur, Sonora). Variety tenuispina is a component of the Sonoran Desert flora, occurring in La Paz and Yuma counties in southwest Arizona, Imperial County in southeastern California, and adjacent northwest Mexico.