Mystery Valley is 1.5 miles long and 500 yards wide at its widest point. Its bottom is about 150 feet below the hilltops around it.
The objective of the Michigan Karst Conservancy is to protect karst areas in Michigan and to educate the public about the value of karst lands and the safe and proper use of these lands.
One aspect of this objective is to provide educational trails on its karst preserves. These trails are narrow footpaths that often go through wet or muddy areas; across or around rocks and boulders;and often have steep, narrow, hilly, or sideways tilted surfaces. Some cross bare rock or cross a stream on a narrow rustic bridge.
These trails are not suitable for personal assistance mobility devices such as walkers, manual or motorized wheelchairs, power scooters, golf carts, off-road or all-terrain vehicles. Use of such equipment on MKC trails is not reasonable and is likely to do damage through soil erosion, trail widening, plant and root damage, and is thus prohibited.
Visitation to MKC preserves is at the visitor's own risk. MKC normally will not have staff or volunteers or emergency phones or equipment present at a preserve. The preserves are a significant distance from emergency medical facilities. Cell phone coverage is limited or non-existent, especially in the Upper Peninsula.
To begin, walk east along the fence line to Marker 1.
Marker 1
The open view to the north is across the western end of the valley.
Marker 2
This is the start of Earthcrack Trail. A small swallow hole lies just north of the marker. (A swallow hole is a depression through which surface water goes underground. They are common in Presque Isle and Alpena counties.)
Marker 3
This knoll, Known as "Rocky Top," is the highest point in the preserve.
The exposed bedrock here is the Devonian Alpena Limestone and it underlies all of Mystery Valley. It formed in the shallow waters of a warm, tropical sea that covered Michigan some 360 million-400 million years ago.
Marker 4
The low ridge visible to the south through the young sugar bush forest was made by farmers who piled up rocks from the surrounding fields that were left behind by glacial ice thousands of years ago.
Marker 5
The long, narrow opening in the ground is an earth crack. It formed as the limestone on the down-valley side of the crack pitched or slid into the direction of the valley whose empty space offered no support for the rock.
As the collapse occurred to form the valley, a number of east-west trending cracks developed on the slopes of the valley. Watch for earth cracks on both sides of the trail on your way to Marker 6.
Marker 6
As you proceed west toward Marker 7, the trail follows a narrow ridge between two parallel sets of earth cracks.
The trail to the east leads to Sunken Lake County Park which contains the eastern part of Mystery Valley.
Marker 7
Notice the convergence of two earth cracks.
Marker 8
This the eastern end of the longest, widest and deepest earth-crack on the preserve. Be careful near its edge.
Marker 9
The earth crack here is hundreds of feet long, several feet wide and in some places, nearly 15 feet deep.
Marker 10
Earth cracks at Mystery Valley are visible only on the south slope of the valley.
Notice the several sets of roughly parallel cracks extending down toward the valley floor. Such cracks on the north side of the valley are covered with glacial drift.
Marker 11
Notice the unusually steep drop to the north. This is not a "normal" erosion slope but rather the result of solution followed by collapse that may have happened suddenly.
Marker 12
The boulder beneath the tree on the hill to the left is a glacial erratic. It formed somewhere north of Lake Huron and glacial ice moved it to its present location.
The boulder originated as sand deposited along or near an ancient shoreline, developing over time into sandstone. Heat and pressure during deep burial changed the sandstone to a metamorphic rock called quartzite.
Marker 13
The Valley Trail begins at Marker 14 to the right. To return to Leer Road, turn left and follow the directional arrows.
Look closely at the exposed limestone near the post. It contains fossils of some of the marine life that inhabited the sea in which the limestone formed.
The shells are brachiopods, the lacy-appearing fossils are bryozoa and the small circular disks are part of the stalk of a crinoid.
Follow the two-track down through the forest to the valley floor.
Marker 14
Marker 16 is to your left; markers 17 and 18 are to your right.
The fireplace beside the trail en route to 16 is all that remains of a former picnic ground when Mystery Valley briefly existed as a tourist attraction decades ago.
Marker 15
Water rising from beneath the surface often results in the formation of a lake that covers the west and lowest end of the valley. Most of the water comes up to the surface through an impressive bedrock-walled sinkhole at the west end of the valley (here hidden from view".
Rain and spring thaw adds to the volume of water in the lake.
As water flows through the underground drainage system beneath Mystery Valley toward Lake Huron, the lake drains back down through the sinkhole (now acting as a swallow hole( and disappears. Sometimes the water is sucked down so fast that a whirlpool develops over the top of the hole.
If the valley is dry, feel free to continue west along the trail to view the swallow hole.
The visible pile of broken rock lies around the rim of yet another swallow hole. The broken rock is the result of a former owner's attempt to reach the passages beneath Mystery Valley.
Marker 16
Prior to the building of a dam around 1900, the north branch of the Thunder Bay River flowed into Mystery Valley.
During the 1800s, lumber companies that floated logs down the river and into the lake grew tired of losing valuable timber each time the lake drained away. Whole trees and tons of rock were tossed into the lake in hopes of plugging the swallow hole.
Even when it worked, the fix was only temporary. Seeping water would eventually clear the hole out and the lake would disappear.
Tales of a maze of underground rivers spread rapidly among area residents. The vision of a Mammoth Cave beneath northeast Michigan continues to fascinate many residents of Presque Isle and Alpena counties.
Marker 17
The Alpena Limestone is part of a larger rock formation known as the Traverse Group, which is a mixture of limestone and shale.
The Traverse Group extends to a depth of about 800 feet beneath the floor of Mystery Valley.
Below the Traverse Group is another stack of limestone known as the Detroit River Group which contains anhydrite and gypsum, two minerals that dissolve much faster than limestone. Solution of these two minerals has allowed the overlying Traverse rocks to drop from the level of the surrounding ridge tops to the level of the valley floor on which you now stand.
The kiosk marks the boundary between MKC/MNA property and Sunken Lake County Park. Return to Leer Road via Marker 13.