National Geographic : 1894 Jan 31
168 F. H. Newell-Arid Regions of the United States. The limits are not easy to place, for they depend upon climatic forces which vary in intensity from year to year-that is to say, in any given locality within the arid regions there may not be for several successive years sufficient moisture for maturing crops of grain, while in the following year rain occurring at the right time may enable .a farmer to produce a heavy crop. Thus in the latter year these arid regions might be considered as re duced in size, to be again increased as drought follows drought. It is necessary, therefore, to assume certain arbitrary boundaries based upon considerations of general success or failure of ordi nary agricultural operations in so far as they are dependent upon rainfall. For the eastern boundary it is convenient to assume the one hundredth meridian west of Greenwich, although, as a matter of fact, " dry " farming has been successfully carried on as far west as the one hundred and fifth meridian or even beyond. The western boundary is more irregular, owing to a wide differ ence in the topography of the country which lies between the well-defined arid and humid areas near the Pacific coast. As laid down by Powell* on the maps of the Geological Survey, the southwestern boundary of the arid region is the Pacific ocean up to a point on the coast of California north of Monterey bay. From here the line turns inward across the valley of the San Joaquin, then, excluding the bay counties, follows northward along the western foothills of the Sierra Nevadas and the eastern slopes of the Cascade range of Oregon and Washington, in which latter state it turns eastward, excluding from the arid regions the northeastern portions of Washington and Idaho. These lines, as originally drawn, were based largely upon the assumption that twenty inches of annual rainfall were necessary for farming opera tions, but were modified, however, by considerations of the sea sonal distribution.f The lines thus laid down, although they may be criticised from various standpoints, are sufficiently exact for any general discussion, and are, perhaps, more useful than others drawn with greater nicety and attempting to reach higher precision. * J. W. Powell: Second annual report of the irrigation survey, in Elev enth Annual Report of the United States Geological Survey, part 2, irri gation, Washington, 1891. t Lands of the Arid Regions of the United States, J. W. Powell, Wash ington, 1879, p. 3 et seq.
1894 Feb 14
1893 Jul 10