Distribution. Mountain slopes, dry valleys, and high mesas from northwestern Nebraska and western Texas to the shores of the Pacific Ocean, and from southern British Columbia to Lower California and northern Mexico; extremely variable in different parts of the country in size, in the length and thickness of the leaves, size of the cones, and in the color of the bark. The form of the Rocky Mountains (var. _scopulorum_, Engelm.), ranging from Nebraska to Texas, and over the mountain ranges of Wyoming, eastern Montana and Colorado, and to northern New Mexico and Arizona, where it forms on the Colorado plateau with the species the most extensive Pine forests of the continent, has nearly black furrowed bark, rigid leaves in clusters of 2 or 3 and 3′—6′ long, and smaller cones, with thin scales armed with slender prickles hooked backward. More distinct is Pinus ponderosa var. Jeffreyi Vasey. [Illustration: Fig. 14] This tree forms great forests about the sources of the Pitt River in northern California, along the eastern slopes of the central and southern Sierra Nevada, growing often on the most exposed and driest ridges, and in southern California on the San Bernardino and San Jacinto ranges up to elevations of 7000° above the sea, on the Cuyamaca Mountains, and in Lower California on the Sierra del Pinal and the San Pedro Mártir Mountains. A tree, 100° to nearly 200° high, with a tall massive trunk 4°—6° in diameter, covered with bright cinnamon-red bark deeply divided into large irregular plates, stiffer and more elastic leaves 4′—9′ long and persistent on the glaucous stouter branchlets for six to nine years, yellow-green staminate flowers, short-stalked usually purple cones 5′—15′ long, their scales armed with stouter or slender prickles usually hooked backward, and seeds often nearly ½′ long with larger wings. Occasionally planted as an ornamental tree in eastern Europe, especially the variety _Jeffreyi_, which is occasionally successfully cultivated in the eastern states. Pinus ponderosa var. arizonica Shaw. Yellow Pine. _Pinus arizonica_ Engelm. [Illustration: Fig. 15] Leaves tufted at the ends of the branches, in 3—5-leaved clusters, stout, rigid, dark green, stomatiferous on their 3 faces, 5′—7′ long, deciduous during their third season. Fruit ovoid, horizontal, 2′—2½′ long, becoming light red-brown, with thin scales much thickened at the apex and armed with slender recurved spines; seeds full and rounded below, slightly compressed towards the apex, ⅛′ long, with a thick shell, their wings broadest above the middle, about ⅓′ long and ¼′ wide.