The parking coordinates will take you to a parking lot in the Brown Bridge Quiet Area. Park your Geomobile at the recommended parking lot and take the trail to the west to ground zero. This will bring you to a platform overlooking the Boardman River valley. There is closer parking but the recommended lot is where you will end up when you complete your field trip.
On the platform, you are at the crest of of a glacial moraine. Take time to observe the river valley. The area below you was a white pine forest at the beginning of the 19th century. It was the great forests which drew Horace Boardman and other lumbermen to the area. Lumbering, and once the land was cleared, farming, brought eastern and European immigrants to the area in the 1850's. In 1921 the valley was flooded when the Brown Bridge Dam was constructed. The dam was built to provide electricity to the city of Traverse City. Observe the location of the river in relation to the moraine and look south to see distant hills.
Many millions of years ago, Michigan was covered by a series of shallow seas which over hundreds of centuries, deposited sheets of sedimentary rock such as shale, limestone, and sandstone which now form Michigan bedrock.
In the Pleistocene era, just over a million years ago, extreme cold winter temperatures turned the moisture in the atmosphere to snow which fell heavily. The summers were not long enough or warm enough to melt the snow completely. These conditions of heavy snow and little thawing persisted for many thousands of years. The weight of the fresh snow turned the lower layers to ice. This process or forming a thick ice sheet took as much as a hundred years. As the ice build up into super thick sheets or glaciers, these ice sheets slowly pushed to the south.
As many as twenty times sheets of ice, one as deep as 2.4 miles thick slowly moved south like a huge bulldozer, plowing, scraping, and grinding the bedrock and carrying boulders, pebbles, sand and soil along with it embedded in the ice. The ice sheets plowed down the states of the midwest, one pushed as far south as the Ohio River valley.
Periodically, there would be a warm spell which would cause the ice sheet to halt it's advance, gradually melt and slowly retreat. As the melting began, and the ice turned to liquid, the water flowed off in streams and rivers while the sand and silt formed what are called outwash plains. As it melted and retreated to the north, at the face of the glacier, a huge lineal ridge of sand and gravel was left behind to mark where the front of the glacier had been. This ridge is called a moraine.
This pattern of slow advance and retreat continued for nearly a million years. The last glacial southern push is called the Greatlakean. It occurred just a little more than a thousand years ago. The southern most terminal of this advance was just here, just south of Grand Traverse Bay, in Grand Traverse County. This Earth Cache asks you to examine this terminal moraine.
From the viewing platform, walk a slight distance to the west to site #11. Here you will take a path down the face of the moraine to a two track trail which runs along the base of the moraine. Follow this trail east to coordinates N44 39.109 W085 29.830. You are walking along what was the bottom of the pond when the dam was active. Along side of you, at the base of the moraine was the edge of the pond. Notice the stones along the edge that was the shore line. These originated as chunks of bed rock many hundreds of miles to the north. The glacier plowed them up and tumbled them along as it advanced. Rain and melting snow washed these down the face of the moraine and the wave action of the pond exposed them. Take a moment to see how many different types of rock you can spot.
At the coordinates you will see some erosion down to the river. Take a look at the soil and stone which has been exposed. Your only task now is to climb the stairs to the north of you back to the parking lot and email the answers to the questions.
To get credit for this Earth Cache, send an email answering the following questions;
1) Describe what you observed from the viewing platform, or if you'd rather, post a picture.
2) Describe four different rocks/stones you see at the base of the moraine. Identify the types if you can.
3) Describe at least three different soil types in the erosion at the base of the stairs. Identify them if you can
4) Take a reading of the elevation at the bottom of the steps and another at the top. What is the height of the moraine?
Bonus - Keep your mind on the idea that the topography in this area is the result of glaciers. Drive north on Arbutus Lake road about 4 miles. You will be driving past a number of post glacial features. Imagine how they might have been formed. Jog left on Hammond to Five Mile Road, as you continue north, observe the edge of the moraine as you wind your way down to East Grand Traverse Bay