View images from the Great Smoky Mountains to the Grand Canyon, Mount Rainier to Kings Canyon and Glacier Bay. As the United States grew and its population expanded and settled westward, regions of the country that displayed natural beauty and ecological diversity became a source of pride. An idea formed that these areas should be maintained and protected for all to enjoy as part of the country’s heritage. This idea would develop into the National Park System over the next 150 years. There are now 58 National Parks and 333 National Monuments and Historic Sites in the United States.