Yellowstone may be the world's first National Park, but the Yosemite Valley and the Giant Trees of Mariposa Groves happen to be the first large-scale area of public lands set aside for protection.
On our trip there this summer, we happen to meet Ranger Lauren who took time to explain the features of the Groves.
Throughout the National Park System, the Division of Interpretation provides programs such as this for park visitors. If you've never visited a park and took advantage of a Ranger Talk, here is an example of what you might find.
Yosemite National Park: www.nps.gov/yose