Thence, crossing the range by the lowest passes, it descends to the eastern base, and pushes out for a considerable distance into the hot volcanic plains, growing bravely upon well-watered moraines, gravelly lake basins, arctic ridges, and torrid lava-beds; planting itself upon the lips of craters, flourishing vigorously even there, and tossing ripe cones among the ashes and cinders of Nature's hearths.
The average size of full-grown trees on the western slope, where it is associated with the Sugar Pine, is a little less than 200 feet in height and from five to six feet in diameter, though specimens may easily be found that are considerably larger.

I measured one, growing at an elevation of 4000 feet in the valley of the Merced, that is a few inches over eight feet in diameter, and 220 feet high.
Where there is plenty of free sunshine and other conditions are favorable, it presents a striking contrast in form to the Sugar Pine, being a symmetrical spire, formed of a straight round trunk, clad with innumerable branches that are divided over and over again.

About one half of the trunk is commonly branchless, but where it grows at all close, three fourths or more become naked; the tree presenting then a more slender and elegant shaft than any other tree in the woods.

The bark is mostly arranged in massive plates, some of them measuring four or five feet in length by eighteen inches in width, with a thickness of three or four inches, forming a quite marked and distinguishing feature.
The needles are of a fine, warm, yellow-green color, six to eight inches long, firm and elastic, and crowded in handsome, radiant tassels on the upturning ends of the branches.

The cones are about three or four inches long, and two and a half wide, growing in close, sessile clusters among the leaves.
[Illustration: PINUS PONDEROSA.] The species attains its noblest form in filled-up lake basins, especially in those of the older yosemites, and so prominent a part does it form of their groves that it may well be called the Yosemite Pine.
Ripe specimens favorably situated are almost always 200 feet or more in height, and the branches clothe the trunk nearly to the ground, as seen in the illustration.
The Jeffrey variety attains its finest development in the northern portion of the range, in the wide basins of the McCloud and Pitt rivers, where it forms magnificent forests scarcely invaded by any other tree.
It differs from the ordinary form in size, being only about half as tall, and in its redder and more closely furrowed bark, grayish-green foliage, less divided branches, and larger cones; but intermediate forms come in which make a clear separation impossible, although some botanists regard it as a distinct species.