Memorial Day weekend, the official kick-off to summer travel, also marks the prime season for visiting many of our stunningly diverse 419 national park sites. It also serves as an opportunity to recognize the individuals who have shaped our National Park System and fought for the conservation of parks over the decades – as well as the important work that is still to come.

It’s difficult to imagine what America would be like without Yellowstone or the Statue of Liberty. National parks offer us more than hiking trails, beachfronts and mountaintops. In these treasured places, we find a sense of identity and inspiration. They speak to who we are as a country and preserve stories of Americans, in places including the Belmont-Paul Women’s Equality National Monument, Cesar E. Chavez National Monument and Stonewall National Monument.

Our national parks also offer veterans, active duty members and their families places of solace, healing and reflection, while also honoring their service. More than a quarter of our national park sites recognize and interpret military history, including Little Bighorn Battlefield National Monument or Gettysburg National Battlefield. Stories of our military past can also be found in places like Yellowstone, where African American soldiers often referred to as “Buffalo Soldiers” of the 25th Infantry served as some of the first guardians of Yellowstone following its designation in 1872.

Beyond park boundaries, these treasured lands play an important role as economic drivers. A new National Park Service report released this week shows that 4.1 million visitors to Yellowstone in 2018 spent $512.6 million in gateway communities, supporting more than 7,000 jobs.

Our national parks do not exist as they do today by accident. Today, grizzly bears roam through Yellowstone, Grand Teton and Glacier, and Florida Panthers prowl the Everglades; and visitors do not look past Yellowstone’s Roosevelt Arch to see industrial mining operations. For as long as we have celebrated our national parks, individuals from all walks of life, conservation organizations, business leaders and elected officials have joined together to speak up for these priceless places.

One of those organizations is the National Parks Conservation Association, (NPCA) which for 100 years has served as the citizen voice for our national parks. The idea for NPCA came at the urging of the first National Park Service Director Stephen Mather and his colleague Robert Sterling Yard, who knew that national parks needed a voice, separate from the federal government, whose sole responsibility was to protect and enhance parks for present and future generations.

Anyone who has been fortunate enough to experience the wonder of national parks wants that same experience for those who will come long after them. Those early park advocates must have felt the same way more than a century ago. Today, each of us serves as the beneficiaries of their vision and action.

Our national parks continue to face tremendous threats, including climate change, attacks on the Endangered Species Act, encroaching energy development, pollution that is harming park air and water, inadequate federal funding and a list of repair needs that is nearly $12 billion across the entire National Park System. These incredible places are also threatened by attempts to derail policies and laws that are meant to protect our most treasured places — from carving up our national monuments for destructive development to fast-tracking oil and gas leasing in and near some of America’s last truly wild places.

During its centennial year and for the next 100 years to come, NPCA encourages all who value our national parks, wildlife and wild places to join us in standing up for the places we cherish. Join us at www.npca.org/100.

Stephanie Adams is associate director of the Northern Rockies Region for the National Parks Conservation Association.