In writing about the increased popularity of national parks in the United States, such as Yosemite, Yellowstone, and the Grand Canyon, environmental economist Margaret Walls wrote:
When one person’s visit to a park doesn’t appreciably diminish the experience for others, the fee to use the park should be zero. That doesn’t apply when the public good starts to experience congestion problems . . . the Park Service should . . . [charge] a significantly higher fee at the most popular parks during the summer months.
Are Yosemite and other national parks public goods? Briefly explain.