Hesperocyparis macnabiana occurs in California at 300 to 850 meters in elevation; preferred habitats are in chaparral and foothill woodland, often on serpentine. It forms the only known cypress hybrid with Sargent cypress.
This species has a generally shrubby growth form to 12 meters in height; the champion specimen in Amador County has achieved a height of 17 meters. The crowns are dense and broadly conical. Bark is rough, furrowed and fibrous. Branchlets are comblike. Leaves exhibit a conspicuous, pitlike, abaxial gland that produces a drop of resin. Pollen cones are two to three mm long by two mm wide. Seed cones are globose, generally 1.5 to 2.5 cm in size, brown or gray, and not glaucous. The light to medium brown seeds are two to five mm long, and occasionally appear slightly glaucous. Among North America's true Cypresses, the MacNab cypress alone manifests flattened branchlets lying all in one plane.