![]() ![]() The line Powell noted as dividing the arid and humid sections of the continent has become known as the “effective” 100th meridian. This amount of rainfall per year is about the minimum that permits farming without irrigation, and it also greatly influences the types of crops that can be grown. In his 1878 “ Report on the Lands of the Arid Region of the United States,” Powell identified the “arid region” as the land west of the 51-centimeter-per-year rainfall line, which closely tracked the 100th meridian. The 100th meridian also corresponds roughly to the 600-meter elevation contour as the land rises from the Great Plains toward the Rockies. states, forming a partial boundary between Oklahoma and Texas. This line, the 100th meridian, runs from pole to pole and cuts through six U.S. In 1878, without benefit of the Landsat program, GPS or Google, and just a decade after the creation of the National Weather Service, John Wesley Powell first advanced the idea that the climatic boundary between the United States' humid East and arid West lay along a line “about midway in the Great Plains” - almost exactly 100 degrees longitude west of the prime meridian in Greenwich, England. ![]() The Great Plains are well known for their sweeping grasslands, which, to the east, eventually turn into great farms, and, to the west, give way to deserts and mountains. ![]()
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