Arch Rock is located on Mackinac Island in Lake Huron. Mackinac Straits has an interesting geological history. Millions of years ago during the Devonian Period ground water produced caves in limestone which subsequently collapsed. Blocks of the limestone which formed the roofs filled the caves and on cementation produced a formation known as the "Mackinac Breccia". This new rock is harder then the original limestone. Arch Rock was formed by wave action when Lake Nipissing levels were higher then the current Lake Huron levels. The softer material was eroded away leaving the harder "Mackinac Breccia".
The above waypoint is for the lower position. If you want to take the high road then use: N45 51.464 W084 36.416 The difficulty will still be a 1, but the Terrain will go up to a 3 due to the up hill climb and the distance. The terrain could be easier depending on how you get there (walk, bike, horse).
In season you will find at the upper area of Arch Rock restrooms, a drinking fountain and pop vending machines.
November 2, 2006 update: The logging requirements have been updated for the earthcache. To log this cache, email the owner with the following answers:
There are two identical signs at Arch Rock, one at the bottom and one at the top.
1.) Tell me when the formation of Arch Rock occurred?
2.) Tell me what was the difference in Lake Nipissing's level when Arch Rock was formed and the present day Lake Huron's level?
3.) Tell me the material that forms the arch? (The answer is not Limestone.)
To email your answers please click here to open a new email.
Not required but always a pleasure to see, please post your photographs too.
Here are some links to geology sites that you may find interesting.
Geology and Earth Science Highlights
GSA EarthCaching
EarthCache Masters Get cool pins for placing and finding earthcaches!