Herbs, perennial, rhizomatous, tending to form small clumps by basal offshoots. Culms triquetrous, bulbous, thickened, (20-)30-80(-90) cm × 0.7-1.2 mm, glabrous proximally, becoming trigonous strongly scabridulous on distal angles, clothed with persistent reddish fibers at base. Leaves flat to V-shaped, 20-45 cm × 2-4 mm. Inflorescences: spike 1, loosely ovoid to ovoid-ellipsoid, (1.5-)2.5-7 × (1-)1.5-3.5 cm; rays (1-)2-4, to 6 cm; 2d order rays rarely present, to 2 cm; 3d order rays absent; bracts (2-) 3, ± horizontal, 1-15(-21) cm × 0.4-3.5 mm; rachilla deciduous, wings hyaline, 0.3-0.4 mm wide. Spikelets (3-)8-26, reddish to reddish brown, linear, compressed-quadrangular, 8-18 × (2.4-)2.8-4 mm; floral scales deciduous, 6-16, laterally reddish, medially green, occasionally red-glandular, laterally strongly 3(-4)-ribbed, medially punctate, 1-3-ribbed, ovate-lanceolate, (2.6-)2.8-3.3 × (1.4-)1.6-1.8(-2) mm, apex weakly 3-dentate, mucronulate, with tuft of crystalline prickles, medially glabrous. Flowers: anthers 0.8-1.1 mm; styles 1-1.4 mm; stigmas 1-1.4 mm. Achenes brownish, stipitate, ellipsoid, 1.6-2 × (0.7-)0.9-1 mm, base whitish, stipe to 0.1-0.2 mm, apex obtuse, slightly apiculate, surfaces papillose. Fruiting late summer-early fall. Canyons in pine forests; of conservation concern; 500-1500 m; Ariz.; Mexico (Chihuahua, Durango, Sinaloa, Sonora). Cyperus hypopitys can be recognized by the combination of reddish floral scales and sharp-angled culms.