Looking over the South Rim of the Grand Canyon, Don Stover points out the blues, greens and other pastel colors in the landscape, and then his mind starts racing.

It's the 50-year-old Seattle resident's first trip to the Grand Canyon, and he can't help but think about how early pioneers traveled through the area, how the river cut through the remarkable geologic feature and how the wind played a factor in forming the canyon.

"It's pretty amazing," he said.

Ninety years after it was established as the country's 17th national park, the Grand Canyon still invokes feelings of astonishment and wonder among the 4.5 million people who visit each year. Known for its immense size, beauty and rugged landscape, it has become an icon of the National Park System.