In May, 2010, the late cacher, brummelbear, hid the first of a series of challenge caches in Michigan for finding the oldest active caches in each county.
The rules of the challenges are, you can find the cache and write your name in the log any time, but in order to qualify for a find, you must have already found five of the seven listed (or previously listed) oldest caches in that county. If you don't yet qualify, your log must be a "write note". Your log should include the list of five or more caches you have found and the dates you found them so the challenge cache owner can verify that you qualify. Newer Michigan County Historical Challenge caches will have a project-gc checker that you can use to verify your results.