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During the ice ages, the massive glaciers that covered much of North America carved out the physiography of the continent. As the glaciers receded and melted, the rivers of the West that we recognize today emerged in their free-flowing forms. These rivers supported the Native American populations that migrated from Asia, providing them both food and a means of transportation that they used to move further inland and create extensive trade networks. In recent centuries, these rivers have been extensively transformed by man through means such as straightening, dredging, diverting their waters through artificial channels, and creating water reservoirs through dam construction. Although many of these alterations have created benefits like flood control, the generation of electricity, and the expansion of agricultural economies, they have ...

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