The Keyhole: Fort Hill EarthCache
A cache by BiT Message this owner
Hidden : 6/3/2008
Difficulty:
1.5 out of 5
Terrain:
4 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:


This EarthCache highlights a unique geological feature within the Fort Hill State Memorial. This EarthCache was developed under Special Permit (#E0208) from the Ohio Historical Society. This park is open Daylight Hours Only and the Collection of Specimens, Either Biological, Cultural, or Mineral is Strictly Prohibited. Fort Hill is closed during deer gun season which is usually the last week in November. Please stay on designated trails, see trail map by clicking here.

Remember as always, Leave No Trace.


Parking (included as a child waypoint) is available at the Fort Hill State Memorial Parking Lot at N 39 07.297, W 083 23.791. To get the most enjoyment of this beautiful area I would suggest making a large anti-clock wise loop. That way you’ll get to see the historic log cabin and spectacular views of the Baker Fork Gorge or trek up Reeds Hill and Jarnigan Knob. You can start by taking Gorge Trailhead (included as a child waypoint) at N 39 07.364, W 083 23.811. Then just past Sunset Run you’ll arrive at the junction of Deer Trail and Gorge Trail. If you take Deer Trail, that will take you over Reeds Hill and Jarnigan Knob. This will be a bit longer but it will eventually bring you close to one of your goals. If you decide to continue on the Gorge Trail, that will take you to the log cabin and on to spectacular views of the gorge. You’ll want to continue to follow the Gorge Trail to the Fort Trail, be sure to take the northwest junction of the Fort Trail. This will go off to the northwest then turn back toward the northeast close to where the trail crosses the fort wall. Then just follow the Fort Trail and it will take you back to the parking area. In all total, your hike will be between 5-8 miles.

The Keyhole


The Keyhole is the second largest natural arch in the State of Ohio. The Keyhole is 77’ long, 35’ high, and only 2’ wide at its narrowest point. Like Rock House, the largest natural arch, The Keyhole is also a natural bridge and a natural tunnel. It provides the only route for Bridge Creek which drains a portion of the nearby Jarnigan Knob.

How do you define a natural arch?

An arch is a horizontal remnant of exposed bedrock supported at two opposing locations spanning an opening created by erosion. Not every hole in the bedrock is considered an arch. An arch must meet this measurement criterion. The span (horizontal measurement of the opening) and clearance (vertical measurement of the opening) must be greater than or equal to 6 feet with neither measurements being less than a foot.

How do you define a natural tunnel?

A natural tunnel is a natural arch whose width, the horizontal measurement perpendicular to the front face of the arch, is greater than or equal to three times its span.

How do you define a natural bridge?

A natural bridge is a natural arch that spans a valley formed by erosion. A natural bridge is always a natural arch, but a natural arch may not be a natural bridge.

How did the The Keyhole form?

During the past Illinoisan glaciations, some 240,000 years before present, the Baker Fork Gorge was formed. The gorge was formed as a result of an ice dam that blocked the north-flowing steams creating a large meltwater lake. As the lake level continued to raise, it eventually reached A level where it began to spill over gaps in the surrounding topography. This spillover began eroded the upper layers of Ohio shale and exposed the underlying Peebles dolotmite that comprise valley walls of the Baker Fork Gorge. As the spillover continued to erode deeper into the gorge, Bridge Creek continued to erode and lowered its level until it reached a vertical crevice which offered a shortcut to Baker Fork. The stream continued to erode the weaker portions of the Peebles dolotmite creating The Keyhole.


To claim a find, please email me the answers to the questions below. Also you will need to upload a picture of yourself holding your GPSr with The Keyhole in the background with your find log. Logs that do not follow the finding requirements will be deleted.

Question 1: Briefly describe the flow rate of Bridge Creek through The Keyhole and how do you think it got its name?

Question 2: How far is The Keyhole located from Baker Fork




Sources:

Camp, Mark J.
2006 Roadside Geology of Ohio.Mountain Publishing Company, Montana.

Hansen, Michael C.
1988 Natural Bridges in Ohio, Ohio Geology.

Potter, Martha A. and Thomas, Edward S.
1970 Fort Hill. The Ohio Historical Society, Ohio.

Additional Hints (No hints available.)



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