Forest physiography; physiography of the United States and principles of soils in relation to forestry . rmations of the Basalt Cover Although the basalt plains of the Columbia region were formed in anearly horizontal position and although these plains appear to beapproximately horizontal to-day, there are in reality many importantdepartures from horizontality. The Snake River plains are now in theform of a broad trough or downfold reaching from Lost River andSawtooth Mountains on the north to Goose Creek and Bear RiverMountains on the south. Many minor irregularities of structure havebeen not
Forest physiography; physiography of the United States and principles of soils in relation to forestry . rmations of the Basalt Cover Although the basalt plains of the Columbia region were formed in anearly horizontal position and although these plains appear to beapproximately horizontal to-day, there are in reality many importantdepartures from horizontality. The Snake River plains are now in theform of a broad trough or downfold reaching from Lost River andSawtooth Mountains on the north to Goose Creek and Bear RiverMountains on the south. Many minor irregularities of structure havebeen noted. In southwestern Idaho the lavas and intercalated lake 1 W. Lindgren, The Gold and Silver Veins of Silver City, De Lamar, and other MiningDistricts in Idaho, 20th Ann. Kept. U. S. Geol. Surv., pt. 3, 1898-gg, p. 77. See this authorsgeologic map, Plate 8, p. 76, for the distribution of the various types of rocks found in a little-known section of central Idaho south of the National Forest that lies east of Mount Idahoand northeast of the Snake River Valley. COLUMBIA PLATEAUS AND BLUE MOUNTAINS 199. 200 FOREST PHYSIOGRAPHY and river sediments have been gently flexed and, near the bases of thebordering mountains, broken and faulted.^ These structural irregu-larities are of considerable economic importance, for it is upon thetrough-like arrangement of the beds that the artesian condition of thedeeper waters depends. The economic development of the region hasbeen accomplished to a notable extent by the use of artesian watersfor domestic purposes and for supplying stock as well as for a smallamount of irrigation. The existing relation of drainage to relief implies antecedent con-ditions on the part of the streams. The lava, originally disposed inan essentially horizontal position, has been deformed from this positionbut the deformation has not proceeded so rapidly as to rearrange thedrainage courses Stream courses laid out upon the nearly, flat lavasheets in response to the initia
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectforestsandforestry
