"We save wild places so they might one day save us," writes Kim Heacox, author of The National Parks: An Illustrated History, a new book from National Geographic that looks back at the history of parks.
These photos from the book demonstrate the enduring power of preservation.
Ten Thousand Smokes
In 1916, a National Geographic expedition in southeast Alaska explored the "Valley of Ten Thousand Smokes," as explorer Robert F. Griggs called the volcanically active area. It would become Katmai National Monument.
Carlsbad Caverns National Park in New Mexico includes 119 known caves, which were made when natural sulfuric acid dissolved the surrounding limestone.
A Wizard's Island
Crater Lake National Park was authorized in 1902 in southern Oregon. The ancient crater is filled with blue water, and it hosts Wizard Island.
President Teddy Roosevelt (left) and conservationist John Muir take in the view of Yosemite on a camping trip on Glacier Point. Both men advocated for the protection of wilderness.
More than three million people visit the iconic Mount Rushmore National Memorial in South Dakota every year. The carving took 14 years and 400 workers. It was completed in 1941.
A hiker explores the sand dunes of San Miguel Island, in California's Channel Islands National Park. The park was established in 1980, although two of the five islands were protected as a monument starting in 1938.
Rocky Mountain High
Dedicated in 1915, Rocky Mountain National Park protects a quintessential Colorado landscape. In this early image, hikers enjoy the scenery of Longs Peak.
Remember the Alamo
The historic missions of San Antonio, Texas, are protected as a national historical park. The Alamo is the most famous, but several other structures stand testament to a period of Spanish colonialism.
This 800-foot (240-meter) spire in Canyon de Chelly National Monument in Arizona is thought by the Navajo to be the home of the mystical Spider Woman, who protects the good and punishes the wicked. The monument was designated in 1931.
In picturesque rural Pennsylvania, Gettysburg National Military Park protects the site of one of the most important battles of the Civil War, when the tide turned for the North. In this historic image, visitors survey the scene from Little Round Top.
She Sells Seashells
The national park system also includes a handful of national seashores, including Fire Island, off the southern coast of New York's Long Island. Cars are still banned on much of the island.