CACHE IS NOT LOCATED AT THE POSTED COORDINATES!!
This cache is a bonus for completing the 'Lincoln Highway - Iowa, Clinton County' Adventure Lab. You need to have the Adventure Lab application on your iPhone or Android phone to find this cache.
The Adventure Lab can be found here:
Lincoln Highway - Iowa, Clinton County
This link will take you to a page where you can download the app and/or this Adventure Lab. At one of the locations of the Adventure Lab, you will be provided with the Certitude keyword required to receive the final coordinates for this cache. If you have already completed the Lincoln Highway - Iowa, Clinton County Adventure Lab, just check your Journal for the necessary information!!
For a brief, but fascinating history on the Lincoln Highway click here:
Lincoln Highway Association
and then follow the Iowa Byways/Lincoln Highway signs throughout Iowa!! 
Sidebar trivia: Have you ever wondered why so many East/West streets in communities along Highway 30 are named "Lincoln Way"? Because of the Lincoln Highway, of course!! 
The final location of this cache is within 100 feet of the 1913 original route of the Lincoln Highway. The difficulty level of this cache is based on completing the required stages of the Adventure Lab.
Actual difficulty level at GZ is 1.5.
GOOD LUCK, HAVE FUN, AND HAPPY CACHING!!
You can validate your puzzle solution with certitude.