The sixth competition in the X Marks the Spot series should be rather less of a challenge than the previous one. This feature, located in western North Dakota, is a well-known landmark that has given rise to much Native American and modern-day folklore. The landform is of a type that is quite rare in North Dakota, and unlike many of the larger and more extensive examples of its kind, this one was formed by slope failure rather than dissolution.

1. What is the geologic (i.e., geomorphic) feature marked by the X?
2. By what name is this feature "formally" known?
3. What is the name and approximate age of the rock formation in which this feature occurs?