Plants without sterile culms; loosely cespitose, with rhizomes to 2 cm long, 2-3 mm thick. Culms (40) 50-92 cm, sometimes branched, sparsely to densely scabrous; nodes 2-3. Sheaths and collars smooth or scabrous; ligules (3) 4-7 (9) mm, obtuse, lacerate; blades 10-38 cm long, (2) 3-4 (7) mm wide, flat, scabridulous, adaxial surfaces glabrous or sparsely hairy. Panicles (4) 7-16 (18) cm long, (0.7) 1.1-2 (3) cm wide, nodding, contracted, pale green to purple-tinged; branches 1-5 (6.5) cm, sparsely to densely scabrous, usually spikelet-bearing to the base. Spikelets (4) 4.5-6 mm; rachilla prolongations 1-2 mm, hairy throughout, hairs 1.5-2.5 mm. Glumes keeled, mostly smooth, keels slightly scabrous distally, lateral-veins obscure, apices acuminate; callus hairs 2-3 mm, 0.5-0.6 times as long as the lemmas, somewhat sparse; lemmas 3.5-5 mm, 0.5-1.5 mm shorter than the glumes; awns (0.5) 1-1.5 (2) mm, attached to the upper 2/5 of the lemmas, not exserted, slender, straight, easily overlooked when short; anthers (1.8) 2-2.7 (3) mm. 2n = 28.
Colo., N.Mex., Utah, Mont., Ariz., Wyo.
Calamagrostis scopulorum grows on canyon slopes and wash bottoms, and in dry to moist montane to alpine habitats, often on rocky, sandy to silty soil, at 1000-3550 m. It grows from western Montana and Wyoming south to Arizona and New Mexico.
"decumbent" is not a number.