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Petroglyphs and Potholes EarthCache

Hidden : 05/03/2008
2 out of 5
3 out of 5

Size: Size:   other (other)

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Geocache Description:

Located at the Sanilac Petroglyphs Historic State Park. The terrain is generally flat with only small elevation changes. Some areas of the trail can be wet and muddy.

First off some information about this area. Etched into a sandstone outcrop by prehistoric artists, these rock carvings were first discovered after a forest fire swept through Michigan's Thumb area in 1881. Native Americans created this unusaul artwork 300 to 1,000 years ago. The petroglyphs provide a glimpse into the lives of an ancient woodland people who once occupied this area. They are the only known rock cravings done by Native Americans in Michigan.

A couple of times per year the enclosure that surounds the petroglyphs are open for a closer viewing. Please check out this site for complete details on when this will happen. According to that web site the next time will be:
June 28, 2008
OPEN HOUSE 9 am-3 pm
Historical displays, Interpreters and programs.

Saniliac Petroglyphs State Historic site encompasses 240 wooded acres. A one-mile self-guided walking trail that twice crosses a meandering stream and passes by the ruins of a 19th century logging camp and a 110 year old white pine tree.


  • A. Enter the fenced area when the entery gate is closed.
  • B. Walk upon or otherwise come into contact with the petrolyphic rock within the fenced area.

I brought you to this area to learn about potholes. Not the kind that Michigan drivers learn to avoid while driving. The potholes you will learn about are created by nature, in nature. Potholes can range in size from a few inches around and deep up to 42 feet in diameter to 38 feet deep.

Potholes are found around the world. Some are found in rivers and the process that created them can be activity seen. In the usual interpretation, potholes are considered to be the effects of erosion by streams and rivers over very long periods of time. The actual work of abrasion is considered to have been done either by hard grains of sand held in suspension by the rapidly flowing water; or by large boulders, called "grinders," in the bottom of the pothole, that were agitated constantly by the currents swirling around inside. The tiny grains in the rapid currents are thought to have gradually worn down the rock into a depression, that was deepened by the motion of the grinders.

Other potholes are found far from flowing water or are found well above the reach of flowing water. Potholes that occur far from streams and valleys, sometimes high up on hillsides and mountains, are explained by geologists as the effects of the great ice ages of the Quaternary. Supposedly, during this time, there were potholes formed when the ice melted, as rivers flowed underneath the ice and on its surface. Sometimes these surface rivers plunged down a crevasse, and eroded the bedrock beneath, forming potholes on the most unlikely places.

The published waypoint is for the parking area. To claim your find on this earthcache you must complete the following tasks:

  • 1. How many potholes you see at waypoint #4?
  • 2. What has happened to potholes you see at waypoint #5?
  • 3. What is the width and depth of the pothole you find at waypoint #6?
  • 4. How many potholes you see at waypoint #7?

Not required but always a pleasure to see, please post your photographs too.

All of the eight child waypoints are located on the trail. There are some spur trails that lead to a pothole area. Stay on the trails!

To email your answers please click here to open a new email.


Additional Hints (Decrypt)

Qba'g ybbx sbe gurz ba gur ebnq.

Decryption Key


(letter above equals below, and vice versa)