This box is accessible only after finding the Hypnocachemachia Alethiometra geocache.
Clues: From the final stage of the Hypnocachemachia Alethiometra geocache, walk back along the Corps of Engineers boundary to the last corner you passed. If you stop at the corner, a very small 3-ringed tree will be at 12:00. At around 11:00 are two large pine trees. Behind the larger one under some leaves is the box.