Leaves ovate or oval or sometimes nearly orbicular, rounded or acute at apex, especially on vigorous shoots, gradually or abruptly narrowed and cuneate at base, finely or sometimes coarsely and occasionally doubly serrate, slightly thickened and reflexed on the somewhat undulate margins, when they unfold pale green and covered with deciduous matted white hairs, at maturity dark green and lustrous on the upper surface, frequently marked, especially on the midrib, with minute glandular dots, light yellow-green and slightly puberulous below, 2′—3′ long, 1½′—2′ wide, with a stout yellow midrib and primary veins; petioles slender, yellow, hairy, flattened and grooved on the upper side, ½′—¾′ long; stipules ovate, acute, scarious, puberulous, about ¼′ in length. Flowers: staminate aments in slender-stemmed pubescent clusters, usually short-stalked, during the summer dark olive-brown and lustrous, ¾′—1′ long and about 1/16′ thick, beginning to lengthen late in the autumn before the leaves fall, fully grown and 4′—6′ long and ¼′ thick in January, with dark orange-brown scales, and deciduous in February before the appearance of the new leaves; calyx yellow, 4-lobed, rather shorter than the 2 or occasionally 3 or rarely single stamen; pistillate aments in short pubescent racemes emerging from the bud in December, their scales broadly ovate and rounded. Fruit: strobiles oblong, ⅓′—½′ long, with thin scales slightly thickened and lobed at apex, fully grown at midsummer, remaining closed until the trees flower the following year; nut broadly ovoid, with a thin margin. A tree, frequently 70°—80° high, with a tall straight trunk 2°—3° in diameter, long slender branches pendulous at the ends, forming a wide round-topped open head, and slender branchlets marked by small scattered lenticels, at first light green and coated with pale caducous pubescence, soon becoming dark orange-red and glabrous, and darker during the winter and following summer. Winter-buds nearly ½′ long, very slender, dark red, and covered with pale scurfy pubescence. Bark on old trunks 1′ thick, dark brown, irregularly divided into flat often connected ridges broken into oblong plates covered with small closely appressed scales. Wood light, soft, not strong, brittle, close-grained, light brown, with thick lighter colored often nearly white sapwood. Distribution. Banks of streams from northern Idaho to the eastern slope of the Cascade Mountains of Washington and southeastern Oregon, and southward from the valley of the Willamette River, Oregon (near Salem, Marion County, _J. C. Nelson_) over the coast ranges and along the western slopes of the Sierra Nevada to the mountains of southern California (San Bernardino, San Jacinto, and Cuyamaca Ranges); the common Alder of the valleys of central California, occasionally ascending on the southern Sierra Nevada to altitudes of 8000°, and the only species at low altitudes in the southern part of the state.