50 Most Popular National Monuments

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40. Sunset Crater Volcano National Monument
> Average annual visitors: 181,370
> Location: Arizona
> Established: 5/26/1930
> Purpose: Marks volcanic cinder cone created around 900 years ago.

Source: Thinkstock

39. Wupatki National Monument
> Average annual visitors: 203,440
> Location: Arizona
> Established: 12/9/1924
> Purpose: Protects red sandstone pueblos built between 1120 and 1250.

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Cities With the Most Idle Youth

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38. Organ Pipe Cactus National Monument
> Average annual visitors: 205,456
> Location: Arizona
> Established: 4/13/1937
> Purpose: Protects the only place in the U.S. where organ pipe cactus grows wild.

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37. Craters of the Moon National Monument
> Average annual visitors: 211,684
> Location: Idaho
> Established: 5/2/1924
> Purpose: Marks a landscape shaped by 2,000 year-old lava flows.

Source: Wikimedia Commons

36. Fort Frederica National Monument
> Average annual visitors: 240,630
> Location: Georgia
> Established: 5/26/1936
> Purpose: Preserves British colonial fort that withstood a Spanish attack.