Cache is the bonus for Rathdrum Prairie Oddities Lab Caches. Cache is almost a literal park and grab, but your arms aren't that long. And I don't know what you're driving.
Rathdrum Prairie Oddities Lab Caches can be found here: Rathdrum Prairie Oddities Caches
By completing the lab caches, you will be able to get the pieces required to decode the cache. Cache is a short drive away from the lab caches. The bonus cache can be found at :
N 47 4A.BCD W 116 5E.FGH