Trees to 10m; trunk to 0.5m diam., straight, much branched; crown dense, becoming rounded. Bark red-brown, irregularly furrowed and cross-checked to irregularly rectangular, plates scaly. Branches spreading to ascending, persistent to trunk base; twigs slender, pale orange-brown, puberulent-glandular, aging brown to gray-brown. Buds ovoid, light red-brown, ca. 0.4--0.5cm, slightly resinous. Leaves (3--)4(--5) per fascicle, persisting 3--4 years, (2--)3--6cm ´ (1--)1.2--1.7mm, curved, connivent, stiff, green to blue-green, margins entire to minutely scaly-denticulate, finely serrulate, apex subulate, adaxial surfaces mostly strongly whitened with stomatal bands, abaxial surface not so but 2 subepidermal resin bands evident; sheath 0.5--0.6cm, scales soon recurved, forming rosette, shed early. Pollen cones ovoid, ca. 10mm, yellowish. Seed cones maturing in 2 years, shedding seeds and falling soon thereafter, spreading, symmetric, ovoid before opening, broadly ovoid to depressed-globose when open, (3--)4--8(--10)cm, pale yellow-brown, sessile to short-stalked, apophyses thickened, strongly raised, diamond-shaped, transversely keeled, umbo subcentral, low-pyramidal or sunken, blunt. Seeds obovoid, body ca. 15mm, brown, wingless.

Dry rocky sites; 1200--1800m; Calif.; Mexico in Baja California.

Pinus quadrifolia is the rarest pinyon in the flora. It hybridizes naturally with P . monophylla .