character: John Wesley Powell
topic: Impact of Dams on River Ecosystems
grade: 9
subject: Geography
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character: John Wesley Powell
topic: Exploration of the Colorado River
grade: 9
subject: Geography
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character: John Wesley Powell
topic: River Conservation Efforts
grade: 9
subject: Geography
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character: Various Scientists
topic: Ecosystem Changes Due to Dams
grade: 9
subject: Geography
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