Rhizomes freely branching, producing dense clumps, slender, 0.5-0.7 cm diam., covered with bases of old leaves; roots fibrous. Stems simple, solid, 2-3 dm. Leaves: basal with blade sometimes pink to red basally, finely ribbed, linear, 3-3.5 dm × 0.5 cm, subglaucous, margins not thickened, apex acute; cauline 1-3, imbricated, mostly free, bractlike, blade linear-lanceolate, inflated. Inflorescence units (1-)2-flowered; spathes often flushed with pink or red, lanceolate, 4-8 cm × 5-10 mm, subequal or unequal and inner somewhat longer than outer, rigid, apex acuminate. Flowers: perianth pale cream with distinct veins of lavender, reddish brown, or brown, margins often distinctly crisped; floral tube funnelform, 3-5.8 cm, slender, then expanding abruptly to base of flower; sepals spreading outward from base and remaining in horizontal position for entire length, narrowly lanceolate to oblanceolate, 4-6.5 × 1.1-1.8 cm, base attenuate into long claw; petals somewhat spreading, not strictly erect, 4.5-6.5 × 0.6-1.4 cm, base gradually attenuate; ovary 1-2 cm, gradually tapering to each end; style 2-3 cm, crests linear, undulate near tip, 1-2.5 cm; stigmas triangular; pedicel 0.8-1.8 cm at anthesis. Capsules oblong, round in cross section, 3-4 cm, base abruptly attenuate into pedicel, apex gradually acuminate into distinct beak apically. Seeds grayish brown, pyriform to oval, 3 mm, wrinkled. 2n = 40.

Flowering Jun--Jul. Dry, sunny woods; Calif.

Iris tenuissima hybridizes with I. chrysophylla, I. douglasiana, I. hartwegii, I. macrosiphon, I. purdyi, and I. tenax.