Culms 10-40(60) cm, stiff, erect; nodes villous. Sheaths villous on the upper margins; blades 5-14 cm long, 3-8 mm wide. Panicles 4-10 cm; branches to 35 mm, with 1-3 spikelets. Spikelets 10-15 mm, persistent. Glumes 9-14 mm; lemmas 7-9 mm. Caryopses about 4 mm long, about 2 mm in diameter. 2n = 20.

Swallenia alexandrae grows on sand dunes in Inyo County, California. It is only known from four sites, all between 900-1200 m, in the Eureka Valley of northern Inyo County. At these sites, it forms dense colonies 1-2 m across. It is state-listed as rare and federally-listed as endangered because of off-road vehicle activity.