Plants densely cespitose. Culms 20-91 cm. Leaves: sheaths adaxially white-hyaline, sometimes gold tinged near summit, summit U-shaped or zigzag to rounded, prolonged to 3 mm beyond collar; distal ligules 1.5-4 mm; blades 3-4 per fertile culm, to 7-30 cm × 1.6-3.9 mm. Inflorescences dense or open, gold to brown, occasionally beaded, 1.7-4.8 cm × 6-16(-23) mm; proximal internode 3.5-7.5 mm; 2d internode 2-5.5 mm, these 2 internodes collectively more than 1/3 as long as inflorescences; proximal bracts usually bristlelike, shorter than inflorescences. Spikes (3-)5-12, distant, loosely aggregated, ovoid to broadly ovoid, 6-14.5 × 2.5-9.2 mm, base rounded to attenuate, apex truncate, rounded, or sometimes tapered. Pistillate scales gold to brown and often reddish, with whitish or green midstripe, ovate to broadly ovate, (2.5-)3.5-4.7 mm, usually shorter than and narrower or as wide as perigynia, margin white, 0-0.2 mm wide, apex obtuse to acuminate. Perigynia ascending, green or straw colored to coppery, conspicuously 6-11-veined abaxially, (0-)4-5(-8)-veined adaxially, veins reaching top of achene, lance-ovate to ovate, plano-convex or biconvex, 3.4-4.8(-5.3) × 1.1-1.6(-2.2) mm, 0.4-0.65 mm thick, margin flat, including wing 0.15-0.4 mm wide, ciliate-serrulate at least on distal body; beak gold to brown, usually reddish, at tip, cylindric, unwinged, ± entire for 0.5-0.6 mm, abaxial suture inconspicuous or with conspicuous white margin, distance from beak tip to achene 1.5-2.5 mm. Achenes elliptic to ovate or, rarely, broadly ovate, 1.5-2 × 0.9-1.3 mm, 0.4-0.6 mm thick.

Fruiting summer. Moist mountain meadows and slopes; 1200-3200 m; Calif., Nev.

Most material from Idaho reported as Carex mariposana is C. abrupta; plants in at least two Idaho localities very closely resemble C. mariposana.