britannica.com
britannica.com
education.nationalgeographic.org
National Geographic Education
https://education.nationalgeographic.org › resource › united-states-regions
kids.britannica.com
en.wikipedia.org
en.wikipedia.org
worldatlas.com
nap.nationalacademies.org
The National Academies Press
https://nap.nationalacademies.org › read › 27213 › chapter › 6
britannica.com
worldatlas.com
nytimes.com
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