GENERAL REMARKS. 9 



and cafions of the numerous mountain ranges composing the interior region, while the valleys are treeless, or, 

 outside of the narrow river bottoms, nearly treeless. The interior forest attains its greatest development and 

 considerable importance upon the western ?slope of the California Sierras and upon the flanks of the high peaks 

 of the southern Eocky Mountain system, from Colorado, where the timber line reaches an extreme elevation of 

 13,500 feet, to southern New Mexico and western Arizona. The minimum in North American forest development, 

 outside the absolutely treeless regions, both in the number of species and in the proportion of forest to entire j 

 area, is found south of the Blue mountains of Oregon, in the arid region between the Wahsatch mountains and '. 

 the Sierra Nevada, known as the Great Basin. Here the open, stunted forest is confined to the highest ridges and 

 slopes of the infrequent canons of the low mountain ranges which occupy, with a general north and south trendy 

 this entire region. The individuals which compose this forest are small, although often of immense age, and 

 everywhere show the marks of a severe struggle for existence. Seven arborescent species only have been detected 

 in the forests of the northern and central portions of this region. The mountain mahogany {Cercocarpus), the ouly 

 broad-leaved species of the region, with the exception of the aspen, which throughout the entire interior region 

 borders, above an elevation of 8,000 feet, all mountain streams, reaches here its greatest development. This 

 tree, with the nut pine {Pinus monophylla), characterizes this region. Stunted junipers are scattered over the 

 lowest slopes of the mountains, or farther south often cross the high valleys, and cover with open growth the mesas, 

 as the lower foot-hills are locally known. An open forest of arborescent yuccas {Yuaca brevifolia) upon the. high 

 Mojave plateau is a characteristic and peculiar feature of the flora of this interior region. The red fir and the 

 yellow pine, widely distributed throughout the Pacific region, do not occur iipon the mountain ranges of the Great 

 Basin. 



The heavy forests of the interior region, found along the western*slopes of the California Sierras and upon the 

 Rocky Mountain system, are, for the most part, situated south of the forty second degree of latitude. The forests 

 of the whole northern interior portion of the continent, outside the region occupied in the northern Eocky mountains 

 by the eastern development of the Coast Forest, feel the influence of insufiBcient moisture; the number of species of 

 which they are composed is not large ; the individuals are often small and stunted, while the forests are open, scattered, 

 without undergrowth, and confined to the canons and high slopes of the mountains. The most generally distributed 

 species of this northern region, a scrub pine {Pinus Blurrayana), occupies vast areas, almost to the exclusion of other 

 species, and is gradually taking possession of ground cleared by fire of more valuable trees. South of the fifty- 

 second parallel the red fir (Pseudotsvga) and the yellow pine (Pinus ponderosa) appear; with them is associated, in 

 the Blue mountains and in some of the ranges of the northern Rocky mountains, the western larch {Larix occidental is),. 

 the largest and most valuable tree of the Columbian basin. 



The forest covering the eastern slope of the Sierra Nevada consists almost exclusively of various species of 

 pine, often of great size and value. The characteristic species of this region are the yellow pine and the closely- . 

 allied Pinus Jeffreyi, here reaching its greatest development. The red fir is absent from this forest, while the oaks, 

 multiplied in many forms on the western slopes of these mountains, have here no representative. 



The forests of the southern Rocky Mountain region, less heavy and less generally distributed than those of the 

 westemJ'slope of the Sierras, are, as compared with those of the Great Basin, heavy, dense, and valuable. They owe 

 their existence to the comparatively large precipitation of moisture distributed over this elevated region. The 

 characteristic species of the Colorado mountains is a spruce {Picea Engelmanni) ; it forms, at between 8,000 and 10,000 

 feet elevation, extensive and valuable forests of considerable density and great beauty; with it are associated a 

 balsam fir of wide northern distribution, and various alpine and subalpine species of pine; at lower elevations 

 forests of yellow pine and red fir cover the mountain slopes, while the bottoms of the streams are lined with 

 Cottonwood, alder, and maple, or with an open growth of the white fir (Abies voncolor), a species of the Coast Forest, 

 here reaching the eastern limits of its distribution ; the foot-hills above the treeless plain are covered with scant 

 groves of the nut-inne (Pinus edulis), stunted junipers, and a small oak, which in many forms extends through a large 

 area of the southern interior region. A forest similar in general features to that of Colorado, and largely comijosed 

 of the same species, extends ver the high mountains of New Mexico to those of western Texas and western and 

 northwestern Arizona, where a heavier forest of pine covers the elevated region lying along the thirty-fltth parallel, 

 culminating in the high forest-clad San Francisco mountains of northern Arizona. 



The species of the interior Pacific region mingle along its southern borders with the species peculiar to the 

 plateau of northern Mexico. The Pacific-Mexican Forest, although differing widely in natural features from the 

 Atlantic-Mexican Forest, possesses several species peculiar to the two. The forests of this region are confined to 

 the high mountains and their foot-hills, and to the banks of the rare water courses. They disappear entirely 

 from the Colorado desert and from the valleys and low mountain ranges of southwestern Arizona. Tbe most 

 important and generally distributed species peculiar to the valleys of this region is the mesquit, the characteristic 

 species of .the Atlantic-Mexican region. The suwarrow, however, the great tree cactus, is perhaps the most 

 remarkable species of the region, giving an unusual and striking appearance to the dry mesas of central and 

 southern Arizona. The high mountain ranges, extending across the boundary of the United States, between the one 

 hundred and fifth and the one hundred and eleventh meridians, enjoy a larger and more regularly distributed rainfall 

 than the regions east, and especially west, of these meridians. The forests which cover these southern mountain 

 ranges are often dense and varied. Upon their summits and almost inaccessible upper slopes the firs and pines of 



