Plants bulbose; bulb coat membranous. Stems not branching, straight. Leaves: basal withering; blade linear-attenuate. Inflorescences 1-flowered, long-peduncled; bracts opposite. Flowers erect; perianth open, turbinate to campanulate; sepals lanceolate, attenuate, ca. 4 cm; petals pinkish, with chevron-shaped, dark red blotch distal to gland, obovate, cuneate, rounded, ca. 5 cm, with few flexible hairs near gland, margins irregularly dentate distally; glands oblong, not depressed, densely covered with slender, unbranched hairs; filaments lanceolate-linear, shorter than anthers; anthers short-tipped. Capsules erect, linear, angled. Seeds unknown.
Phenology: Flowering late spring–mid summer.
Habitat: Vernal meadows
Elevation: 800 m
Calochortus monanthus is known only from a single collection from meadow along the Shasta River, near Yreka, Siskiyou County, by E. L. Greene in June, 1876. It is presumed extinct.