Geomorphology

Introduction

Sunrise over the unique landscape of the crags. Photo by Katie Smith

The Crags are a hidden treasure most noted for their beautiful rock formations. These immense rock structures seem to capture the interest and fascination of those who make the journey to admire them. Located on the west side of Pikes Peak, the Crags are situated about two miles from the Crags Campsite. Summer months attract many more visitors and tourists, but the trails are sparsely used throughout the winter. The unique landscape of the Crags is a direct result from the creation or uplift of Pikes Peak. The main interest in this area are the rock formations which have been sculpted over thousands of years from chemical and mechanical weathering. Weathering and erosion are the two factors which have greatly altered these rock structures. There are also a few geomorphic hazards such as erosion, snow, lightening, and extreme winds that one must acknowledge before making the trek to the Crags. The following picture shows the unique landscape of the Crags at sunrise.

Overview

Interesting rock formation showing the pink granite color in the Crags. Photo by Katie Smith

Pikes Peak is amongst the most famous landmarks in Colorado. Due to its history and prominent stature, many people visit this landmark from around the world.  About one billion years ago, this eminent landscape was created from a block of Precambrian granite, also known as the Pikes Peak Batholith.  As Pikes Peak was uplifted, vertical layers of rock were formed that underwent thousands of years of erosion.  Many interesting rock formations were formed due to the weathering and erosion which took place on this mountain.  These pink, granite rock formations are known as the Crags.  The image at right shows the pink granite color, and the interesting rock formations within the Crags.

Source for this information: Hopkins and Hopkins, 2000

Attraction

Of particular interest here is the protrusion of the Pikes Peak Granite that has undergone chemical and mechanical weathering. One is able to see traces of weathering along the entire trail. The Crags is an easy trail that leads to spectacular views of unusual granite formations on the west side of Pikes Peak. The trail takes you through the meadow foothills, which are filled with Scrub Oaks, Pinon Pines, and Junipers. The foothills will lead you up to the montane zone, where you will pass many Aspens, Ponderosa Pines, and Douglas Firs. The following pictures show the differences between the meadow foothills and the montane zone along the Crags trail. Different rock patterns and rock fractures are the prominent chemical and mechanical weathering features located along the entire trail. 

Source for this information: Hopkins and Hopkins, 2000

Meadow foothills along the Crags trail. Photo by Katie Smith

Montane zone along the Crags trail. Photo by Katie Smith

Geomorphic Processes
The Crags region has undergone chemical and mechanical weathering processes for over a billion years. The Pikes Peak granite measures a total area of about 1,200 square miles within Colorado. Rock composition is important for understanding both chemical and mechanical weathering processes. Chemical and mechanical weathering has structured the Crags into unique vertical spires or horizontal features, due to the amount of fractures within the rock. These breaks provide a plane of weakness which allows water to enter, thus allowing chemical and mechanical weathering processes to occur. 

Chemical weathering involves the complex process that breaks down rock components and internal structures of minerals (Tarbuck and Lutgens pg. 187). The pink color in the Pikes Peak Granite demonstrates the presence of certain minerals such as quartz, feldspar, and mica. These minerals are capable of reacting with different elements such as water or salt, creating the chemical weathering process. (Tarbuck and Lutgens pg. 187). 

The dominant chemical weathering process we see in the Crags is known as hydrolysis. Hydrolysis is the decomposition of any substance with water, in this case, potassium feldspar. In this process, water or hydrogen attacks and replaces the potassium ions in the feldspar structure, which disrupts the crystalline network. Basically, potassium feldspar generates a residual clay mineral, a soluble salt (potassium bicarbonate), and some silica, which enters into solution (Tarbuck and Lutgens pg. 190-193). From the images, one is able to see the effects of hydrolysis in the Crags. The vertical stripes of black on these rock structures display the chemical breakdown from hydrolysis. 

Hydrolosis along the Crags trail. Photo by Katie Smith.

Hydrolosis along the Crags trail. Photo by Katie Smith.

The erosion and transport of quartz into the sandy material in the Crags. Photo by Katie Smith.

Quartz, on the other hand, is the other predominant mineral in granite; which is extremely resistant to weathering. One can identify quartz based on its glassy appearance. When hydrolysis breaks down granite, quartz remains substantially unaltered. So, when granite weathers, the feldspar crystals will dull, and will slowly, over time, turn to clay. The interlocked quartz grains remain intact as they are released from the feldspar, creating a sandy material which is transported through erosion. You will see evidence of this chemically weathered sandy material throughout the Crags. (Tarbuck and Lutgens pg. 190-193). There is an abundant amount of sandy material at the base of this photograph from the chemically weathered boulder. 

The Crags area also experiences physical changes in rock composition through chemical weathering. As water flows through the joints and fractures within a rock, the rock structure eventually takes on a spherical shape. The corners of the rock are attacked on a greater scale due to the increased surface area, which is known as spheroidal weathering. One is able to see rounded or spherical shaped rock structures throughout the Crags, which is chemically weathered from spheroidal weathering. The following pictures show the corners of a giant boulder which hare being weathered at a greater scale. There is one sheet which is in the process of being weathered spheroidally on this boulder. 

Spheroidal weathering in the Crags. Photo by Katie Smith.

Another glimpse of spheroidal weathering directly behind the boulder in the middle of the picture. Photo by Katie Smith.

As the Crags region undergoes mechanical weathering, the rocks are being broken down into smaller and smaller pieces, all of which retain the original material characteristics. This area experiences three dominant forces and characteristics of mechanical weathering, frost wedging, unloading, and gnamma pits.

Frost wedging is the repeated cycle of freezing and thawing of water within a rock structure. Water will work its way into the cracks in rock and upon freezing, expands and enlarges these openings. After many freeze thaw cycles, the rock will eventually be broken into many smaller angular fragments. This process is predominant in mountainous regions, such as the Crags, and usually experiences a daily freeze thaw cycle. One indicator of frost wedging is the talus slope created under a large rock structure. (Tarbuck and Lutgens pg. 185-186). The following pictures display different formations of frost wedging. In the first picture there are many vertical pillars of rock, which look as though they could almost fit together as one giant rock structure. This shape is formed over time from the frost wedging cycle. Water works to break the rock apart, and the outcome is many different pillars of rock separated by the frost wedging fractures. The next picture shows a close up view of the effects of frost wedging. One is really able to see how the two rock structures fit together at one time. 

Frost weathering in the Crags. Photo by Katie Smith.

Close-up view of frost weathering within the Crags. Photo by Katie Smith.

Unloading and sheeting  in the Crags. Photo by Katie Smith

The erosion of a rock due to reduction in pressure is known as unloading. When the Pikes Peak granite is exposed to erosion, concentric slabs will eventually break loose. This process is known as sheeting, which appears to look like multiple layers of granite peeling off, similar to the layers of an onion. These outer layers will expand more rapidly, causing them to separate from the entire rock body. From the picture, one is able to see the effects of unloading and sheeting. You will notice there are many rock slabs which appear to have many different layers, and could potentially slide off the rock. Sheeting is extremely common throughout the Crags and Pikes Peak region. One key characteristic is to look for spheroidal weathered rocks, and usually you will see the results of sheeting. (Tarbuck and Lutgens pg. 186).

Gnamma pits are another characteristic of mechanical weathering within the Crags region. Gnammas, or weathering pits, are depressions which vary in shape and size and typically contain water for a portion of the year. They are usually formed from a weak point or fracture within the rock, and vary from a few centimeters to several meters in length or width. Gnamma pits enlarge from weathering and erosion and are prominent throughout the Crags, as shown in the following two pictures.

Gnamma pit located within the Crags. Photo by Katie Smith

A series of gnamma pits within the crags. Photo by Katie Smith

Weathering occurs in mechanically fragmented and chemically altered rock structures. Chemical weathering involves the chemical transformation of rock into a new compound. Hydrolysis is the dominant chemical weathering process within the Crags region. Mechanical weathering is accomplished through the physical breakdown of rocks, which does not alter the mineral composition. Evidence of mechanical weathering in the Crags is frost wedging, unloading, and gnamma pits. Through understanding these differing weathering processes, one is able to grasp a better outlook of the changing landscape. 

Reference: Tarbuck, Edward J and Frederick K. Lutgens. Earth: Introduction of Physical Geology. Pearson Education Inc., 2005. Upper Saddle River, New Jersey 07458. Chapter 6, Weathering and Soil, pages 184-194.

Hazards
The main geomorphic hazard situated within this area is erosion or rock falls. This hazard is most prominent throughout the winter months due to the freeze thaw weathering process. As ice freezes in rock fractures, the water expands, causing the fracture to expand as well. This process will continue until the fracture eventually breaks loose from the remaining rock. Rock falls will usually take place in the mid-morning or evening, when the ice is melting and freezing. The accompanying picture shows potential areas for rock falls. Take caution during these times as you hike throughout this region.

Other hazards within the Crags area include frequent thunderstorms, blizzards, and high winds.  The Crags area contains numerous rock surfaces that are particularly exposed and thus are vulnerable to lightning. 

Blizzards and severe storms with frequent lightning can manifest rapidly. Once the snow begins falling, hazardous conditions will begin to develop. The Pikes Peak Granite typically becomes icy, and the trail can be difficult to locate. However, the snow does allow for extremely warm shelters called quinzees. The following picture shows a quinzee shelter in the Crags area. 

Rock fall locations in the Crags. Photo by Katie Smith.

Quinzee shelter in Crags area.  Photo by Katie Smith.

Evidence of extreme winds on the summit of the Crags. Photo by Katie Smith.

Due to the altitude and lack of shelter throughout the Crags, extreme winds are capable of blowing trees down and creating dust or rock storms. The picture shows the barren summit of the Crags with two trees struggling to stay alive. One is able to see which direction the wind is most prominent due to the tilt of the trees. Check the weather forecast before heading to the trail, and if the weather turns sour, as it usually does in the afternoon, take cover or head for safer ground. 

Conclusion
A hidden secret located within the Pikes Peak region, the Crags is a vast region which displays many interesting geomorphic processes such as the landscape formation, rock structures or formations, weathering and erosion features, and geomorphic hazards. Through knowing and understanding many of these processes, one is able attain a far greater appreciation for the beauty of this region.

Driving Directions and Google Earth .kmz File
Google Earth Placemark File (.kmz) file: link
Driving Directions from Downtown Colorado Springs:

• To reach the trailhead take Interstate 25 to highway 24W to Divide CO.

• At Divide, head south on highway 67 for 4.3 miles.

• Just past Mueller State Park, take a left on the road that has a sign for the Crags Campground.

• Follow this road to the Crags Campground.

• Turn left into the campground and follow it to the end where you will find a parking lot and a sign for the Crags trail. 

References
Hopkins, R., and L. Hopkins, 2000, Hiking Colorado's geology: The Mountaineers, Seattle, Wash., 239 p.