Soil Formation in Rocky Mountain National Park
In Colorado, United States
Size:  (not chosen)
How Geocaching Works
Rocky Mountain National Park is located west of Estes Park and north and east of Grand Lake. This is a fee area of the National Park Service, and costs $20 per vehicle. This fee is covered in the Rocky Mountain National Park Annual Pass, the Rocky Mountain National Park/Arapaho National Recreation Area Annual Pass, and the America the Beautiful Pass. Please see the following website (visit link) for the entire fee schedule. The park is open 24 hours a day, 365 days a year. Road and Trail Conditions and Closures can be found at: (visit link) Recorded information for the condition of Trail Ridge Road can be found by calling (970) 586-1222. Please remember that all geologic features within the borders of Rocky Mountain National Park are protected by law, as are all natural and historic features. Please do not disturb, damage, or remove any rocks, plants, or animals.
Parking is at the Glacier Gorge Trailhead and the hike is up a well-marked trail. The trailhead parking area is often filled during the summer, and shuttle bus transportation is available at the Bear Lake shuttle bus parking area. The starting elevation is approximately 9250’, so bring sunscreen for the bright sun and extra water for the dry air. Afternoon thunderstorms are always possible in the summer months so plan accordingly.
The aim of this EarthCache is to look at an outcrop of granite from the Longs Peak-St. Vrain Batholith off of the Glacier Gorge Trail, and to examine the processes that are taking place in the formation of soil on this rock. You will then need to find another site along the trail where soil is being formed and describe the process to me in your own words. This trail can be rough in places, so please wear good footwear and watch your step.
Soil is formed from the breakdown of inorganic rock combined with organic materials. Rock is broken down through weathering, which is the decomposition of rocks and minerals through contact with the atmosphere. Weathering is generally classified into two different types: mechanical weathering and chemical weathering.
Mechanical weathering occurs when there is no chemical change in the rock as it breaks down. Forces involved in mechanical weathering include temperature, water, ice, and pressure. The most common type is the freeze-thaw action of water. As water freezes, it expands outward, cracking the rock and increasing the surface area for more weathering to take place. Temperature change is another type of mechanical weathering. Rocks will expand as they are heated and contract when they are cooled. This heating and cooling causes cracks, which can then be exploited by other means of weathering. The force of pressure is most evident in granite exfoliation domes which can be seen in the mountains of Lumpy Ridge, north of Estes Park. These granite domes were once covered by metamorphic rocks which were thousands of feet thick. After the overlying rock eroded away, the granite was exposed and the pressure was released. The outer parts of the rock expanded, causing parallel fractures on the rock surface. This is called sheeting, or exfoliation.
Chemical weathering involves a change in the chemical makeup of the rock. These reactions change the bonds that hold the rock together. This type of weathering is much more active in areas where there is abundant water, which helps to facilitate the chemical reactions. Oxidation, dissolution, and hydrolysis are common types of chemical weathering. Oxidation occurs when oxygen combines with metallic ions to form weaker oxides. The most common example of this is when oxygen and iron combine to form iron oxide (rust). Dissolution occurs when rain falls and combines with gases such as carbon dioxide, sulphur dioxide, and nitric oxides to create weak acids. These acids dissolve cracks in the rock. Hydrolysis occurs when water combines with silicate minerals to form other minerals which are softer than the original rock types. This is what occurs when feldspar in granite breaks down into clay.
A close look at this outcrop will show that biological weathering, a combination of mechanical and chemical weathering, is working to break things down further. Lichens cling to the rock and break down the surface by secreting chemicals and covering portions of the surface with their root systems. Wind-blown soils are caught in small depressions on the rock. Over time, grasses begin to grow in the depressions and help to catch more soil, as well as send down roots of their own. Insects, spiders, and other small animals add organic materials through their feces and bodily remains, helping to enrich the soils which are forming. Eventually, shrubs or trees begin to grow with roots that help to break the rocks down further.
It takes many years to change inorganic rock into a form on which plants can grow. At one time, the rock in front of you was bare with no hint of organic material. Now it is a thriving, living community due to weathering, and the formation of soil.
In order to log this EarthCache, complete the following:
1.) Find the granite outcrop at the coordinates and examine the weathering processes that are taking place. Include with your online log a picture of you at this site.
2.) Find another outcrop, boulder, or rock face along the Glacier Gorge Trail on which weathering is acting to form soil. Using the information given above, send me an email describing the mechanical, chemical, or biological weathering that is taking place to create soil at this site.
3.) In your online log, include the coordinates and at least one picture of you at the site you are using to answer Question 2.
The above information was compiled from the following sources:
2004. Rocky Mountain National Park. In Harris, A.G. et al., editors. Geology of National Parks, Sixth Ed. P. 337-356. Dubuque, Iowa: Kendall/Hunt Publishing Company.
Cole, J.C., and Braddock, W.A. 2009. Geologic map of the Estes Park 30’ x 60’ quadrangle, north-central Colorado: U.S. Geological Survey Scientific Investigations Map 3039, 1 sheet, scale 1:100,000, 1 pamphlet, 56 p.
Colorado Geological Survey. 2003. Messages in Stone. Matthews et al., editors. Denver, Colorado.
Geography4Kids. Weathering. Online at (visit link)
Hopkins, R.L., and Hopkins, L.B. 2004. Hiking Colorado’s Geology. Seattle, Washington: The Mountaineers. 240 p.
KellererLynn, K. 2004. Rocky Mountain National Park. Geologic Resource Evaluation Report. NPS D307, September 2004. Online at: (visit link)
PhysicalGeography.Net. Weathering. Online at (visit link)
Rocky Mountain National Park. Online at: (visit link)
Wikipedia. Weathering. Online at (visit link)
Rocky Mountain National Park was most helpful in the background discussion, aid in the choosing of sites, and review of this EarthCache. My thanks to the Park for allowing the placement of this EarthCache!
(No hints available.)
Last Updated: on 3/11/2013 10:36:57 PM Pacific Daylight Time (5:36 AM GMT)
Coordinates are in the WGS84 datum