Forest physiography; physiography of the United States and principles of soils in relation to forestry . itic masses crumble into particles of quartz, fragmentsof mica, and angular fragments of crystals of rather freshfeldspar. The quartz and mica are washed down thelarger streams by the sudden rains; but the larger frag-ments of feldspar often accumulate upon the alluvialfans and give them a very distinctive appearance. The occurrence of arboreal vegetation in response togreater rainfall and its zonal distribution in response totemperature are here as everywhere in the Southwestinteresting su
Forest physiography; physiography of the United States and principles of soils in relation to forestry . itic masses crumble into particles of quartz, fragmentsof mica, and angular fragments of crystals of rather freshfeldspar. The quartz and mica are washed down thelarger streams by the sudden rains; but the larger frag-ments of feldspar often accumulate upon the alluvialfans and give them a very distinctive appearance. The occurrence of arboreal vegetation in response togreater rainfall and its zonal distribution in response totemperature are here as everywhere in the Southwestinteresting subjects of study. The general geographicdistribution of the many types of vegetation has beenworked out as follows: 248 FOREST PHYSIOGRAPHY (i) Zone of cactus, yucca, agave, scanty grass, 3000 to 3500 luxuriant vegetation in the vicinity of water. (2) Zone of Obione and Artemisia (greasewood and sage-brush), poorgrass, diminished growth of cactus, altitude 3500-4900 feet. (3) Zone of cedar (Juniperus occidentalis), few cactus, 4900 to 6800feet. (4) Zone of pine and fir, 6800 to 10,800 Scale of Miles 1 k i) X 1 Fig. 68. — Waste-bordered mountains of the Arizona Highlands, Camelsback quadrangle, U. S. Note the lack of a permanent stream, the large number of intermittent streams as shown bythe dotted lines, and the ragged character of the mountain slopes. Contour interval, 250 feet. These zones are lower on eastern and northern than on southern andwestern slopes and the amount of canting increases with increasingelevation (p. 293). The quaking aspen is seen below 7500 feet, likewisethe fern {Pteris aguilina). Above 7000 feet the white oak accompanies ARIZONx\ HIGHLANDS 249 the pine but is never found in great quantities, principally in smallpatches or groves. In some instances the pines occur in splendid forests.^ The character of the tree growth in the extreme southern part of theArizona Highlands has been analysed by He found (1893) theMexic
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectforestsandforestry
