Rhizomes 2–3 mm thick. Culms 15–22(–30) cm, 2.5–3 mm thick at base. Leaves: sheaths 2–3 cm, fronts often mottled dark brown; blades flattened laterally, with 5–8 conspicuous air cavities, median groove inconspicuous, elliptic in cross section, 10–20(–25) cm × 0.6–1.2 mm. Inflorescences 1.4–2.5 cm × 7–12 mm, staminate portion 2–10 mm. Pistillate scales white medially, 3–5-veined, shorter and narrower than perigynia, leathery, apex acute to acuminate; proximal scales sometimes awned to 4 mm. Anthers 2–3 mm. Perigynia angles veined, shortly 3–10-veined on faces, sessile, broadly elliptic, 5–7 × 3–4.8 mm, base rounded, apex rounded; beak entire; rachilla longer than fruit. Stigmas 1–2 mm. Achenes stalked to 0.15 mm.

Fruiting Aug–Sep. Dry rocky or gravel slopes; above 2500 m in Calif., above 2000 m in Oreg.; Calif., Nev., Oreg., Wash.

Carex breweri occurs in the Sierra Nevada and Cascade Mountains north to Mt. Hood.

A. Cronquist (1969) considered Carex breweri and C. engelmannii conspecific; he distinguished them at the varietal level by a difference in pistillate scale characters. The correlated differences in perigynium shape and veins, the dimensions of most structures, and the foliar anatomy support their retention as distinct species.