Plants densely cespitose. Culms 35-75 cm. Leaves: sheath summits U-shaped, sometimes prolonged to 2 mm beyond collar; distal ligules 2.5-8 mm; blades 3-5 per fertile culm; 15-45 cm × 2-3(-4) mm. Inflorescences ascending, dense, green to gold or brown, (1-)1.4-2.5 cm × 9-17 mm; proximal internode 1.5-4 mm; 2d internode 1-4 mm; proximal 2-3 bracts erect to ascending, leaflike, the proximal longer than inflorescence, often more than 2 mm wide, base ± surrounding culm. Spikes 5-11, ± individually indistinct, ovoid to broadly ovoid, 7-13 × 5-9 mm, base rounded to acute, apex truncate to acute. Pistillate scales pale gold to red-brown, with pale to green midstripe, lanceolate to ovate, 3.3-4.8 mm, shorter and narrower than perigynia, margin sometimes white, 0.1-0.2 mm wide, apex acuminate to awned. Perigynia ascending to ascending-spreading, green, gold, or sometimes coppery, conspicuously 0-11-veined abaxially, conspicuously 0-8-veined adaxially, ovate to lanceolate, usually flat, 3.5-5 × 1.3-1.75 mm, 0.3-0.5 mm thick, margin flat, including wing 0.2-0.3 mm wide; beak usually gold or red-brown at tip, usually flat, winged, ± ciliate-serrulate or, sometimes, cylindric, unwinged, ± entire for 0.5-0.6 mm, (1.4-)1.7-2.5 mm, abaxial suture inconspicuous or with white margin, distance from beak tip to achene. Achenes stipitate, ovate to obovate, (1.2-)1.5-1.9 × 0.75-1(-1.2) mm, 0.3-0.4 mm thick.

Fruiting late spring-summer. Seasonally wet places, 0-1000 m; B.C.; Calif., Oreg., Wash.

Carex unilateralis intergrades with C. athrostachya.