Forest physiography; physiography of the United States and principles of soils in relation to forestry . old timber line andhave unforested summits. Those having a forest cover at all are en-circled by a band of forest vegetation from the 7000 or 8000 foot level tothe 11,000 foot level, which represents the upper limit of tree all of them there is a notable canting of the timber lines on passing fromthe warmer and drier southern slopes to the colder and moister northernslopes. The difference of level amounts in some instances to a thousandfeet and is always several hundred feet, bein
Forest physiography; physiography of the United States and principles of soils in relation to forestry . old timber line andhave unforested summits. Those having a forest cover at all are en-circled by a band of forest vegetation from the 7000 or 8000 foot level tothe 11,000 foot level, which represents the upper limit of tree all of them there is a notable canting of the timber lines on passing fromthe warmer and drier southern slopes to the colder and moister northernslopes. The difference of level amounts in some instances to a thousandfeet and is always several hundred feet, being lower on the northernslopes. This condition has been especially well described by Merriam.^More recently Lowell has noted that the degree of canting increaseswith increasing altitude and appears to be a function of radiation andinsolation as controlled by area. With increasing altitude there is de-creasing area. The two sides of a cone will therefore show increasinglygreater differences in the limiting elevations of the tree zones and amore marked canting of the vegetation belts and timber lines.^. Fig. 83.—Timber zones on San Francisco Peaks, Ariz., showing increase in the degree of canting withincreasing elevation. (Lowell.) 1 C. H. Merriam, Results of a Biological Survey of the San Francisco Mountain Region inArizona, North Am. Fauna, No. 3, 1890. 2 Percival Lowell, The Plateau of the San Francisco Peaks in its Effects on Tree Life, Geog. Soc, vol. 43, 1911, p. 380. 294 FOREST PHYSIOGRAPHY SAN FRANCISCO MOUNTAINS AND MOUNT TAYLORSAN FRANCISCO MOUNTAINS The San Francisco Mountains are the center of a volcanic field innorthern Arizona that includes seven large peaks and several hundredsmall peaks. Cones and lava flows together cover about 2200 squaremiles of country. San Francisco Mountain, the highest peak in thegroup, rises to 12,700 feet above the sea and has 5000 feet of relativealtitude. Other prominent peaks are Kendrick Mountain, 10,500 feet,and Bill Willia
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