The smallest U.S. national park is Crabtree Falls in Virginia, covering 0.2 acres (not 0.02). It features a 120-foot waterfall—one of the tallest east of the Mississippi.
While tiny in area, it protects a unique geological and scenic resource within the George Washington and Jefferson National Forests.
Note: Some sources cite other micro-parks (e.g., Thaddeus Kosciuszko National Memorial at 0.02 acres), but Crabtree Falls is often recognized as the smallest natural-area national park.