Kayenta - Coal Creek Trail

Coal Creek Trail

Can you see the fins-like layers poking out of the surface on the north side of the highway? Can you notice any other patterns from rocks breaking down?

The unique fins and gullies formed from weathering and erosional processes acting on the rock layer. Within the larger layer of the Kayenta Formation there are thinner sub-layers of varying compositions. Some of these sub-layers contain grains of sediment that are cemented strongly together, making the sublayer more resistant to the weathering and erosion. This causes these layers to be more resistant to breakdown and removal and appear as if they are sticking up out of the ground. In reality, the layers around these fins have simply eroded away at a faster rate.

Kayenta - fins and gullies
The image above shows the fins and gullies of the Kayenta Formation. This layer contains sub-layers of varying hardness and resistance to erosion. Resistant layers stick up as fins. Less-resistant layers are located in the narrow gullies.

Weathering vs Erosion

Believe it or not weathering and erosion are not the same thing. Weathering is the break-down of rock material. Erosion is the movement or transportation of rock material that has already broken down into smaller pieces.

Examples of Weathering

Weathering of rock material can happen in many different ways.

Physical Weathering

  • Ice wedging - water that freezes expands and can wedge rock apart
  • Root wedging - a growing root can also wedge a rock apart
  • Thermal expansion - Rocks expand and contract when they heat and cool

Chemical Weathering

  • Oxidation - rusting of certain minerals from chemical reactions
  • Dissolution - Water slowly dissolves minerals within a rock

As you look around can you find areas where it looks like the rock layers in the canyon walls are breaking down into smaller pieces?

Kayenta - fins and gullies
Abundant cave-like features on the south side of the canyon are the result of chemical weathering. Weak acid can form in both rain and run-off. This can slowly dissolve the natural cement that holds the grains together, causing this rock to break-down in an unusual way.
Kayenta - fins and gullies
On the north side of the highway you might notice that there are plants growing along many of the cracks in the cliff. Plant roots grow and expand slowly over time. As they grow, they can effectively create a wedge that breaks the rock apart. This is an example of mechanical weathering.

Educator Resources

Educators can download resources for teaching on the Coal Creek Trail. 

Download Educator Resources