In 1872, a wondrous region called Yellowstone was set aside as the world’s first national park, giving adventurous travelers access to a geologist’s paradise that seethes with pent-up volcanic forces. As more and more national parks were created—not just in the United States but also in Canada and Mexico—geologists were revolutionizing their field, piecing together a detailed understanding of how the world works. National parks have made these magnificent reminders of the awe-inspiring power of our planet accessible to everyone. Today, there is no better education in the remarkable forces that formed our world than a tour of the national parks of North America. These parks capture a special place in our hearts and draw millions of tourists each year.