Plants densely cespitose. Culms reddish brown to dark maroon at base; flowering stems 20-70 cm, much longer than leaves at maturity, 1-1.7 mm thick, glabrous or sparsely pilose. Leaves: basal sheaths reddish brown, bladeless, pilose; others grading from dark red to green on back, tan-hyaline on front, reddish brown dotted and usually pubescent at apex; blades flat, 3-12 mm wide, usually pilose, more densely so abaxially, margins ciliate. Inflorescences: peduncles of lateral spikes, when present, less than 10 mm, often pubescent; proximal bracts usually shorter than inflorescence; sheaths 5-50 mm; blades 1.2-2 mm wide. Lateral spikes 2-5, 1 per node, usually crowded toward apex and overlapping staminate spike, erect, sessile or pedunculate, pistillate with 20-40 perigynia attached less than 1 mm apart, cylindric, 12-40 × 4-11 mm. Terminal spike staminate, rarely gynecandrous, sessile or very short-pedunculate, 8-30 × 2-5.5 mm. Pistillate scales reddish brown with narrow white-hyaline margins and green midrib, broadly ovate, shorter than mature perigynia, apex obtuse to short-cuspidate, often pubescent on midrib and awn, ciliate distally. Perigynia pale green, blotched with dark maroon at base, dark maroon-brown distally, 2-ribbed and finely veined with to 20 veins, most conspicuous near base, loosely enveloping achene, ellipsoid, 3.7-5.3 × 1-2.2 mm, membranous, base acute, apex narrowing to beak, body covered with long, appressed to spreading hairs; beak bidentate, 1 mm. Achenes substipitate, 2-2.6 × 1.2-1.7 mm. 2n = 50, 52.

Fruiting late spring-early summer. Seeps, stream banks, roadside ditches, wet meadows and slopes, coastal prairies, mixed evergreen forest along the Pacific Coast; 0-600 m; Calif., Oreg.

Sporadic sterile hybrids between Carex gynodynama and C. mendocinensis are well documented. A reported hybrid with C. hendersonii needs further study to confirm parentage.