Surprising facts about national parks

Yellowstone (Photo: National Park Service)

The spotlight is now turned on our national parks thanks to a new documentary by Ken Burns. The National Parks: America's Best Idea, a six-episode PBS series, will premier on Sunday, September 27. And it's available on DVD and Blu-Ray on October 6.

Our national parks have been around for more than a century, but there is still much to learn. Below are just a few surprising facts about some of the most spectacular spots in the U.S.

• Delaware is the only state without a national park, monument, or historic site. California, on the other hand, is home to the most national parks within the contiguous U.S. 


• Crater Lake is the deepest lake in the United States. It was created 7,700 years ago when the 12,000-foot high Mount Mazama collapsed after a huge eruption.


• Yosemite Falls is the highest waterfall in North America.


• Everglades National Park is the only place in the world where alligators and crocodiles live side-by-side. In fact, it was the first national park that was preserved because of its diverse wildlife. 


• Great Smoky Mountains was the most visited national park in 2008, with more than 9 million visitors. It's not surprising when you take into account that 50% of the U.S. population lives within a days' driving distance of the park. Grand Canyon was number two (4.4 million visitors), and Yosemite was the third (3.4 million visitors) most visited national park.


• Mammoth Cave is the world's longest known cave system. More than 367 miles have been explored.


• Yellowstone is the world's first and nation's oldest national park.


• Wrangell-St. Elias is the largest park in the United States. Thaddeus Kosciuszko National Memorial is the smallest.


• Gerald Ford worked as a seasonal park ranger at Yellowstone in the summer of 1936. He is the only U.S. president who ever served as a park ranger.

Check out Yahoo! Green on Twitter and Facebook.