Herbs, perennial, cespitose, 3--6 dm. Rhizomes densely branching. Culms few--20. Leaves basal, (1--)2--3; auricles 0.5--1(--1.5) mm, apex acutish, membranous; blade flat, 5--15 cm x 0.5--1.3 mm, margins entire. Inflorescences 5--50-flowered, somewhat loose, 1--7 cm; primary bract usually longer than inflorescence. Flowers: bracteoles 2; tepals greenish, lanceolate, (3.5--)5 mm; outer and inner series nearly equal; stamens 6, filaments 0.5--1 mm, anthers 0.1--0.3 mm; style 0.1--0.2 mm. Capsules light brown, 1-locular to pseudo-3-locular, ellipsoid, (3--)5--4.5 x 1.2--1.8 mm, nearly equal to shorter than tepals. Seeds tan, ellipsoid to lunate, 5.5--0.7 mm, not tailed. 2n = 80.

Flowering spring--early summer. Moist, usually exposed sites in clayey or sandy soil around springs, along rivers and streams, and around lakes; below 2300 m; Ariz., Calif., Idaho, Nev., Oreg., Wash.

Juncus occidentalis should perhaps be considered a robust variant of J. tenuis.