YELLOWSTONE NATIONAL PARK, WYOMING - MAY 24: An aerial view of visitors walking around Grand Prismatic Spring in the Midway Geyser Basin on May 24, 2026 in Yellowstone National Park, Wyoming. Grand Prismatic Spring is the largest hot spring in the United States at more than 300 feet wide at its widest point and over 120 feet deep. The colors outside the pool`s blue center are created by "thermophiles"—heat-loving microscopic organisms which flourish in many of Yellowstone’s hot springs. Yellowstone National Park became the nation’s first national park on March 1, 1872, when President Ulysses S. Grant signed a congressional act protecting the land “for the benefit and enjoyment of the people.” Today, the 2.2-million-acre park thrives as part of one of Earth`s last nearly intact large temperate ecosystems, famously preserving over 10,000 hydrothermal features and around 500 geysers—roughly 50 percent of the world’s total. Boasting the largest concentration of mammals in the lower 48 states, Yellowstone stands as the only place in the U.S. where bison have roamed continuously since prehistoric times. Native American communities inhabited and conserved the lands for over 10,000 years, with 27 individual tribes recognized by the National Park Service as carrying modern-day and historic ties to Yellowstone. National Park Week will celebrate America’s 250th anniversary with a weeklong celebration in August featuring hundreds of commemorative events at many of America’s 433 national parks under the theme “Celebrate America’s Story”. Mario Tama/Getty Images/AFP (Photo by MARIO TAMA / GETTY IMAGES NORTH AMERICA / Getty Images via AFP)