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Iron Horse Speleothems EarthCache

Hidden : 08/16/2012
2 out of 5
2 out of 5

Size: Size:   not chosen (not chosen)

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Geocache Description:

For this earthcache, you will need the following equipment: a 50 lumen or brighter flashlight and a camera capable of taking low light photography.  You will be traveling into a nearly blackout tunnel with no light for most of the day.

Coordinates will take you to the entrance of the Iron Horse Tunnel.

The Iron Horse State Park trail was constructed from the western section of the Milwaukee, St. Paul and Pacific Railroad bed and is part of the John Wayne Pioneer Trail. There are 30 substantial trestles, 4 tunnels.  The one you are visiting is 2.3 miles long and is commonly called the “Iron Horse Trail.”  This tunnel section was carved by hand through solid limestone with hundreds of workers and tens of thousands of man hours carving the passage.

The tunnel was constructed from 1912-1914 by the Chicago, Milwaukee, St. Paul and Pacific Railroad, also known as the Milwaukee Road, as part of its line from Chicago to Seattle. Electrification in 1917 eliminated smoke dissipation issues.  In 1980 the Milwaukee Road received approval from the Interstate Commerce Commission to abandon its western lines. On March 15, 1980, the final Milwaukee Road train passed through the tunnel. Later, Washington State acquired the right-of-way for recreational use.

Today the tunnel is part of the Iron Horse State Park rails-to-trails project. It is usually closed between November 1 through early May due to ice formations inside the tunnel. On July 5, 2011 the tunnel re-opened after 11 months of renovations. The $700,000 renovation added a 4-inch layer of concrete to the walls and ceiling, a reinforced structure, and a new and improved walking surface of crushed rock.

The overlying bedrock was once an ancient sea floor.  Millions of years of sediments, shells, bones and minerals created hundreds of feet of limestone west of the supercontinent Pangaea.  Limestone is high in a mineral called calcium carbonate. 

Hundreds of millions of years ago, Pangaea started to break up sending North America westward to run into the Juan de Fuca ocean plate.  This was a collision of Titans: and Juan de Fuca lost.  It was pushed under the North American plate and this area started to become dry land.  The shallow ocean was raised.  Volcanoes formed around the area and ash, cinders and lava now covered the landscape.  Volcanic debris is usually high in sulfur.  Over the next several million years, this area continued to get pushed up to the level you are now.

The sediments were changed through heat and pressure to limestone.  Igneous and sedimentary rocks formed above them from the volcanoes.  Because the uplifting, folding from continents crashing into each other and the earthquakes from volcanic activity, the bedrocks formed cracks and fractures.  Water seeped from above and started to dissolve rock above and deposit in the cracks below.

Fast forward millions of years.  The tunnel you will soon be traveling is a man-made cave: a hollow spot below the surface of the earth.  Water enters the surface above this location, it slowly dissolves the minerals. The mineral rich water moves through the cracks to this cavern.  As water finds cracks, it drips to the floor below, leaving some of the minerals behind.  This process happens over and over as long as there is a supply of water and minerals. The main mineral in this type of process is calcium carbonate, remember where that came from.

The minerals left behind start to form a sedimentary rock called speleothems.  The faster a speleothem is created, the more fragile, the slower, the more stable. 

Stalactites are speleothems that grow from the ceiling.  Cone stalactites are slower growing, cone shaped.  Soda straws are fragile, tubular stalactites usually about the diameter of water drops and fast growing.  Pearls are round, pebble like.  Curtains look like waving fabric along the ceiling.

Stalagmites are speleothems that grow along the floor.  They can look like mushrooms, buttons, donuts, dinner plates, cones or just cover the floor in layers.

Flows are speleothems that from along the wall.  Flows look like frozen water falls.  Flowers look like delicate moss or plants.

Columns are formed when a stalactite and stalagmite connect in a cavern.

Speleothems are considered a national treasure no matter where they form!  Please do not try and remove any from this tunnel.

Along this entire two mile trek, you can find speleothems.   To log this earthcache, you must send an email with the following information.

  1. Line 1: Iron Horse Speleothems: GC3TT7R

  2. Locate speleothems in this tunnel.  From your observations, what type of speleothems do you find?

  3. What kind of obvious speleothem is missing?  Why do you suppose this main category is missing?

  4. What colors do you observe of the speleothems?  Form a hypothesis: what is causing these colors?  Why supports your hypothesis?

  5. Find the longest speleothem from the ceiling you can find.  Make an estimate of its length.  The section of the roof you are looking was completed in July 2011, how fast (inches/year) is this speleothem growing?

  6. Since speleothems are considered a national treasure, help make a record of the structures in this tunnel.  To do this, you will need a camera capable of taking pictures in low light environments.  Take a picture of any speleothem you can find, record the estimated distance from the entrance and where you found the structure. Post your pictures with the distance from the entrance in the description.

Sources: Wikipedia, Washington State Parks and Recreation, United States Geological Society.

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