Which of the following is a National Monument designated under the National Monuments Act?

Devils Tower is designated as a National Monument under the National Monuments Act, which was enacted in 1906 to protect significant natural and cultural landmarks. The designation of Devils Tower as a National Monument in 1906 marked the first time a site was preserved for its geological significance, demonstrating the government's commitment to protecting unique natural formations. The tower itself is notable for its striking geological features and is culturally significant to several Indigenous tribes, many of whom consider it sacred.

In contrast, the other options are national parks, which have a different designation and require a different process for establishment and protection. National parks like Yellowstone, Yosemite, and Badlands were established to preserve larger ecosystems and landscapes and are managed under different regulations that focus on preserving natural beauty and recreational opportunities. National Monuments, such as Devils Tower, often protect specific natural or historic features, allowing for focused conservation efforts.