IowaAdmin: Somehow I overlooked this when I originally approved it. But since this on property managed by the U.S. Army Corps of Engineers, you'll need to get permission. According to other geocachers, they don't seem to have a problem with geocaching as long as you apply for a permit BEFORE you place a cache. The permit states that a Geocache Placement Permit application must be completed and approved by the appropriate Corps of Engineers office before posting the cache on a geocaching website. Each office sets their own rules for this type of thing.
The permit is good for 1 year. After that date, the cache must be re-permitted or removed.
They also say that "Unauthorized cache(s) on Corps of Engineers land will be removed and the responsible person may be cited under the Federal Code of Regulations, Title 36, Part 327."
The reasoning is the security issue. They want to know what is where on their land and who is coming and going and why.
If you would like an application, you can email Jeff Rose - Jeffrey.W.Rose@usace.army.mil and they will send one to you.