Near the parking area is a marquee with more information about the Michigan Karst Conservancy. There are pamphlets located there too. Please use one while walking the trails. Numbered post will guide you through the preserve. Please stay on the marked trails. Due to the geologic activity deep under ground, Earth cracks are present here. Some are big, others are small. Stepping into one could be fatal. If you can, please return the pamphlet back to it's holder for the next vistor.
Things you will need to log this Earthcache:
- GPS
- Camera (optional)
The logging requirements for this Earthcache are:
E-mail me, via my profile, the answers to the following questions:
- Is the flat central area (just west of the posted waypoint) of the valley filled with water?
- If so, estimate the depth of the water.
- If the valley floor is dry, walk to the child waypoint of "SINK".
- Once there, is there water in the sink?
- On your walk from the parking area to the posted waypoint you walked down one side of the valley. Can you describe any area that looked like it has been affected by the collapsing of the under lying bedrock.
- A photo can not be required, but is always appreciated.
Evaporite
A sedimentary rock composed primarily of minerals produced from a saline solution as a result of extensive or total evaporation of the water.
Anhydrite
Is a mineral composed of anhydrous calcium sulfate, CaSO4. Most frequently found in evaporite deposits with gypsum.
Gypsum
Is a mineral composed of calcium sulfate dihydrate, CaSO4·2H2O. Most frequently found in evaporite deposits with gypsum. Gypsum is moderately water-soluble. Gypsum is anhydrite with two water molecules.
Geological History
Centered under Michigan's lower peninsula is a depressed or subsided area that's known as "The Michigan Basin". Around the Basin were other landforms that controlled the flow of sea water in to and out of the Michigan Basin.
The Paleozoic era (540 to 251 million years ago) was a long, quiet period of slow earth movement. Oscillations of sea level caused 24 to 30 minor retreats and transgressions of the sea across the Great Lakes region. At times the seas were warm and clear, supporting a myriad of shelled creatures, at other times the seas were muddy, receiving great volumes of fine silts and decayed vegetation from low lying land. At times desert conditions prevailed, and the seas became excessively salty supporting little life, or were brackish with gypsum, sulfide and chloride minerals. At other times the sea became a shallow, huge swamp that supported vegetation. Each sea left its records in the sediments on its floor. The sediments compacted to rock. The floor of each sea became the basin of its successor, thus each sea was smaller and within the boundaries of its predecessor. Eventually the Michigan basin was filled with a succession of shallow bowl shaped rock formations, one within the other. A variety of sedimentary rock layer formed, such as sandstone, limestone, shale, rock salt, gypsum, anhydrite.
Since the Paleozoic era (541-252 million years ago) ground water has made it's way down into the depths of the Michigan Basin rock layers through faults and cracks. A thick layer of Devonian limestone and shale, known as the Traverse Group, underlies area. Below that, about 800 feet deep, lies the Detroit River Group, which contains large amount of the evaporites anhydrite and gypsum. These minerals dissolve much more readily than limestone, and as the Detroit River Group rocks erode, caverns are created. The Traverse Group rocks above, collapse into the caverns. This collapsing continues all the way to the surface.
The Detroit River Group.
Unlike a valley carved by a river, Mystery Valley was formed by the collapse of the surface into a labyrinth of subterranean chambers created by the water erosion of rock below. Mystery Valley is 1.5 miles long, 500 yards wide at its widest point and about 100 deep, making it one of the largest known collapse valleys in the Great Lakes region.
Water rising from beneath the surface often creates a lake that covers the west and lower end of the valley. Most of the water reaches the surface through a sinkhole in the bedrock at the west end of the valley, which can be hidden from view. Rain and snow melt add water to the lake. As water flows through the underground drainage system toward Lake Huron, the lake drains back through the sinkhole (now acting as a swallow hole) and disappears. Sometimes the water drains so quickly a whirlpool forms over the sinkhole.
This cache is located within the Mystery Valley preserve, which is owned and managed by the Michigan Karst Conservancy. All of the preserves managed by the MKC are free to visit. Parking is allowed only in the designated areas. Always practice Cache In, Trash Out.
References used:
- http://www.geo.msu.edu/geogmich/MIbasin.html
- http://www.caves.org/conservancy/mkc