Forest physiography; physiography of the United States and principles of soils in relation to forestry . ar sea level, now uplifted to a great height.^ Though peneplanationmay be safely inferred from the discordance between the plane of thesublevel hilltops and the structure, the region is nevertheless deeply dis-sected by the rejuvenated streams. Canyons have been formed of such 1 W. T. Lee, Geology and Water Resources of Owens Valley, California, Water-SupplyPaper U. S. Gaol. Surv. No. i8i, igo6, p. 25. 2 The peneplain of the western slope of the Sierra Nevada was first recognized by Gilbert
Forest physiography; physiography of the United States and principles of soils in relation to forestry . ar sea level, now uplifted to a great height.^ Though peneplanationmay be safely inferred from the discordance between the plane of thesublevel hilltops and the structure, the region is nevertheless deeply dis-sected by the rejuvenated streams. Canyons have been formed of such 1 W. T. Lee, Geology and Water Resources of Owens Valley, California, Water-SupplyPaper U. S. Gaol. Surv. No. i8i, igo6, p. 25. 2 The peneplain of the western slope of the Sierra Nevada was first recognized by Gilbert(G. K. Gilbert, Science, vol. i, 1883, pp. 194-195). Diller showed that the planation wasprobably accomplished during Miocene time (J. S. Diller, Tertiary Revolution in Topographyof the Pacific Coast, 14th Ann. Rept. U. S. Geol. Surv., pt. 2, 1894, pp. 404-411). Healso found that gravel deposited upon this peneplain had been elevated, faulted, and tilted,the degree of vertical displacement along the eastern face of the range being 3000 feet at thenorthern end. CASCADE AND SIERRA NEVADA MOUNTAINS 169. Fig. 40. — Typical portion of Yosemite Valley, showing cliffed margins, waterfalls, flat floor, and mean-dering stream. Partly stream eroded, partly ice eroded canyon whose details of cliff structure aredue to geologic structure. (Matthes, Yosemite Valley Map, U. S. Geol. Surv.) lyo FOREST PHYSIOGRAPHY profound depth and steepness as to constitute the chief scenic feature ofthe range outside the snow-capped High Sierra. The main streams such as the Merced, Tuolumne, Feather, and Hetch-Hetchy flow in canyons from a half mile to a mile deep. The encan-yoned portions of the streams are but fractions of the total lengths of thestreams, since the canyons do not appear either at the headwaters orin the foothill belt. They are limited to the intermediate levels wherethe alpine glaciers once occupying the largest valleys produced theirmost important topographic effects. All the canyons h
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