The oxbow lake known as Carter Lake was once a part of the Missouri river. From this point, the river flowed from the north-northwest through what is now the western end of the lake. In July 1877, extensive erosion near the portion of the Missouri River known as Saratoga Bend allowed the river to re-route itself through a channel that became the present river's course.
This map from 1875 shows Saratoga Bend (circled), the course of the river today (arrow), and the approximate location of the cache (star).
