Plants loosely cespitose, with-out rhizomes, with short extra-vaginal tillers. Culms 60–100 (150) cm, erect, glabrous; nodes usually exposed. Sheathsclosed for less than 1/3 their length, glabrous or scabrous, shredding into fibers; ligules 0.3–1.5 mm; blades 3–6(10) mm wide, flat, lax, margins scabrous, abaxial and adaxial surfaces glabrous, adaxial surfaces sometimes scabrous, veins 13–25, ribs obscure; abaxial sclerenchyma in narrow strands; adaxial sclerenchyma developed; girders or pillars formed at the major veins. Inflorescences 10–20(40) cm, open or somewhat contracted, with 1–2(3) branches per node; branches lax, more or less spreading, spikelets borne towards the ends of the branches. Spikelets 7–12 mm, with (2)3–5 florets. Glumes lanceolate, scabrous at least on the midvein, acute to acuminate; lower glumes (1.5) 2.5–4(4.5) mm; upper glumes (3)4–6.5 mm; calluses wider than long, glabrous, smooth or slightly scabrous; lemmas (5)6–8(9) mm, lanceolate, scabrous or puberulent, acuminate, unawned or awned, awns to 2 mm; paleas about as long as or shorter than the lemmas, intercostal region puberulent distally; anthers 1.6–2.5 mm; ovary apicespubescent. 2n = unknown.
Festuca sororia grows in open woods and on shaded slopes and stream banks, at 2000–3000 m. It is restricted to the United States, growing from central Utah and Colorado to Arizona and New Mexico. A single puzzling specimen is the basis for the reported occurrence of this species in Missouri (Yatskievych 1999).