Plants densely cespitose, with-out rhizomes. Culms (45) 60–100(120) cm, glabrous, smooth or scabrous below the inflorescence. Sheaths closed for less than 1/3 their length, smooth or scabrous, persistent; collars glabrous; ligules 2–5(9) mm, entire or lacerate, not ciliate; blades 1.5–3 mm wide, 0.8–1.8 mm in diameter when conduplicate, deciduous, abaxial surfaces scabrous, adaxial surfaces scabrous or pubescent, veins 9–15, ribs 7–13; abaxial sclerenchyma a more or less continuous band; adaxial sclerenchyma present; girders usually formed at the major veins, sometimes only pillars present. Inflorescences (7)10–15(17) cm, open, with 1–2(3) branches per node; branches 4.5–9 cm, lax, erect or spreading, spikelets borne towards the ends of the branches. Spikelets (8)10–14 mm, with (3)4–5(6) florets. Glumes unequal to subequal, ovate-lanceolate, scabrous or smooth, acute; lower glumes (2)3.5–5.5 mm; upper glumes (2.5)4.5–6.5(7) mm; lemmas 6–10 mm, lanceolate to ovate-lanceolate, scabrous or smooth, unawned, sometimes mucronate, mucros to 0.2 mm; paleas shorter than to as long as the lemmas, intercostal region puberulent distally; anthers 3–4.5 mm; ovary apices densely pubescent. 2n = 28, 42.
Festuca thurberi is a large bunchgrass of dry, rocky slopes and hills, open forests, and meadows in montane and subalpine regions, at (1000)2000–3500 m. Its range extends from southern Wyoming south through Utah and Colorado to New Mexico.