Glacial evidence in the Mount Zirkel Wilderness, Colorado

Rick Moran - December 2006

ES 767, Quaternary Geology, Emporia State University


Colorado has 7 regions where permanent snow and ice bodies have been identified, including 14 named glaciers (Hoffman, 2006).  Among these is the Park Range which includes the Mount Zirkel Wilderness.  The total area of all the snow / ice bodies is about 4.8 km2 .  On September 1, 2006 I hiked into the Mount Zirkel Wilderness on the continental divide just south of Mt. Zirkel with the intent of seeking out evidence of past and current glaciation.  Along the way I observed glacial lakes, gouging, striations, snow fields, rock slides, snow melt springs, and paraglacial landforms.  The features I observed appeared to contain no active glaciers, but rock glaciers may have been active during the Little Ice age.




Mt. Zirkel is located 25 miles NNE of Steamboat Springs, Colorado, USA.   The first US expedition in the general area was led by John Fremont in 1844 into what was part of the Ute tribe territory.  The area was named after Ferdinand Zirkel in 1874 for his work in geology.  He also lived near the base of the mountain.  Zirkel was a leading contributor to the advancement of mineralogy in Germany though his microscopic study of rocks by thin section.  Early on he attempted to show minerals could be identified by texture, but changed his approach leading to modern optical mineralogy (Ross, 1942). 


In 1964 the area was designated the Mount Zirkel Wilderness Area within the Routt National Forest.   Expansions of the wilderness occurred in 1980, 1984, and 1993 and now cover 160,000 acres.  The area includes the continental divide in northern Colorado.  Online topography maps are available along with hybrid maps covering the wilderness .  Within the wilderness are more than 70 lakes, valleys, rivers, and varied vegetation.  At lower elevations are lodgepole pines, aspen groves and sagebrush meadows.  Higher in elevation are Englemann Spruce, Subalpine Fir, and finally alpine tundra above 10,400 feet.  The lowest elevation in the wilderness is at 7,400 feet and the high point is Mt. Zirkel.  At 12,180 feet Mt. Zirkel is one of 15 peaks over 12,000 feet in the wilderness.  Within the wilderness are 170 miles of trails.  Just west of the wilderness is the Routt Divide blow down where on October 25, 1997 over 20,000 areas of old growth trees were toppled over when winds approached 100 mph (Snook, 1999 and Scott, 2003)


The surface geology at higher elevations consists of quartz monzonite and metavolcanics of Proterozonic age.  The lower areas are cover with Quaternary till. Some thrust and normal faults have been mapped.


My hike began at Slavonia trail head 4.5 miles SW of Mount Zirkel at an elevation of 8400’.   The trail head is named after the small gold mine settlement that was abandoned in the 1920’s (Mandres, 2000).  One nearby mine is known as the Tom Thumb.   From there I headed east along trail #1150, the Wyoming Trail, also called the Gold Creek Trail past Gold Creek Lake.   The trail branches off into #1142, also called the Red Dirt Pass trail, which I followed NE to Red Dirt Pass at an elevation of 11,550’.   From the pass I hiked a mile to the NW near the base of Mount Zirkel and a mile to the SE along Flattop Mountain at 12,000’.  Along the way I made short side treks to investigate features of interest.  Upon my returned I followed the same trails back to Slavonia.  In all I covered 21 miles over 9 hours.


Topography map with trails hiked.


Recent landforms


One question I was trying to answer is if rock glaciers exist on the Frying pan Basin along the flanks of Flattop Mountain and Mount Zirkel.   There are several variations in the definition of a rock glacier and many examples around the world.   Usually the definition includes active flow with a poorly sorted mix of rock, debris, and ice (Whalley et al, 2003).  They occur in high mountain terrain and resemble small glaciers.  They have small flow rates typically less than 1 meter per year.  The movement has been modeled as overriding, plug-flow, and mixed-flow (Leysinger, 2003). One definition specifies that the ice is hidden, so at the surface only the rock and debris is visible.  The term has also been applied to similar looking features on Mars.  Three main theories have been proposed for their existence:  1) from cirque glaciers, 2) permafrost action rather than glacial, and 3) more of a landslide.   A paraglacial term is also applied to a rock glacier to specify more of a landslide induced movement. (Humlum, 2005) .


I concluded the currently developing ice / snow landforms are paraglacial, but likely had rock glaciers modifying the landscape as recent as the Little Ice age.  Due to time constraints I was unable to ascend up from the base of the larger snow fields, but I was able to observe them at a distance from multiple advantage points from above.   Along the east side of Mount Zirkel are several paraglacial landforms and permanent snow fields.


Along the east side of Mount Zirkel are several paraglacial landforms and permanent snow fields.  Mount Zirkel is the highest peak.


A view of the larger snow field above showing the terminus and debris field below.   Further down is a stream with a small alluvial fan system.


On the east side of Flattop Mountain are several similar features.


This view is looking directly down unto the snow field of the previous photo.    At the base is Peggy Lake formed from a cirque glacier which is now just the permanent snow field.   I did approach the snow field from above, but found I couldn’t get closer than 5 meters without risking sliding down.   The upper 3 meters of the snow field is ice of approximately 30 cm in thickness thinning out to nothing at top.


A number of protalus ramparts are present.   Protalus ramparts are composed of angular rock fragments and are located just beyond the talus toe.  They form as a ridge several feet high and have a width of 10 to 30 feet.  The ridges can be convex to straight (USGS).   They are formed from rocks sliding down from above across persistent snow fields and continue to add to the rampart (Hall, 2006).


A rampart is present at the down slope edge of the permanent snowfields. 


This snowfield is in the trough just upslope from a rampart.  Rocks trails are visible in the snow from debris falling from above adding to the rampart.


The snowfield has a glacial pond at the terminus dammed by a rampart.


Furrowing is present in some of the unconsolidated sediments near the base of some snow fields.  The furrowing appears as elongated narrow troughs parallel to downward flow and look similar to furrows from a plowed farm field.  They imply an active rock glacier existed no later then the Little Ice age and possibly developed more recently.


Furrowing is present at the base of a current snow field.

In the area are examples of several large landslides.


View of a landslide off the slope on the left side of the image.  The rock pile on the right side has climbed partial up the opposite side of the valley.


Close up of the 10 meter high rock pile of the previous photo.  The surface of the pile is composed of angular rocks typically 20 to 50 cm across.

The landscape continues to be modified by many spring feed streams and frost action working angular rocks down slope.


The headwaters of one of many springs originating at the base of a steep mountain slope with permanent snow fields above.


The gently slopping sides near Mount Zirkel display elongated rock piles due to frost action.


Old Landforms


Examples of Roche Moutonnees, a type of stoss-and-lee topography, are located 1 mile NW of the glacial Gold Creek Lake in the valley.  The term Moutonnee comes from the curled wig of barristers.  A Roche Moutonnee is bedrock that is smoothed and rounded on one flank and irregular and steep on the other.  They are formed through a combination of glacial abrasion and plucking (Collins et al, 1999).


The up-valley side of a stoss is smooth and nearly flat.  Along the trail they were polished along the edge as is curves over into the steeper lee side.  The stoss side is smoothed from pressure melting and abrasion.  Glacial plucking is present along the steeper lee flank.   Multiple steps down are present on the lee side those spacing is a function of the bedrock jointing.


Displayed is a small section of a Roche Moutonnee near the base of the valley’s steep sides.  The Roche Moutonnee is stepping down from the narrow side sides of the valley.  It also has striations perpendicular to the steeping down on the lee side.  Polish, plucking, and quarrying are visible in the bedrock.  This outcrop is in a valley 1 mile wide and 5 miles long. 


This outcrop has experienced glacial movement from 2 directions.  It developed from glacial movement coming down from the steep narrow section of the valley right of the photo forming the Roche Moutonnee.   The striations and polish are from glacial abrasion from movement into the photo from the long axis of the valley.


Concentric gouges on the lee side of a Roche Moutonnee.


Of curiosity is a boulder and possibly bedrock in photo 193 that displays striations located on the uphill side of a persistent snow field.


South of Mount Zirkel and west of Red Dirt Pass are much smaller snow fields with their southern exposure to the sun.  Below are several springs that feed a small stream.  The upper valley below is displays evidence of pass rock glaciers, rock movement by frost action, and moraines from past mountain glaciers.

The glacial lakes in the area range from small ponds to several acres in size.  Some show signs of recent modification and others are well established.


Peggy Lake is the larger of the 3 lakes in this chain with moraines in-between each lake.


Gold Creek Lake located 4 km down from the head of the valley.  It was likely formed during Wisconsin glaciation.




The area has many examples of glacial and erosion processes that have occurred.  The landscape has been modified from multiple glacial periods and recent erosional processes.  Among them are paraglacial landforms, permanent snow fields, and Roche Moutonnees.  Since my observations were only of 1/3 of the snow fields I cannot say if rock glaciers exist nearby.  Looking beyond just the area’s scenic beauty, many of the processes and landforms can be identified.




Collins, K., Keely, O., Taylor, C., 1999.  Terrestrial Glacial Features - Erosional Landforms


Hall, Adrian, 2006. Protalus Rampart


Hoffman, Matt, 2006. Glaciers of Colorado


Humlum, Ole, 2005. The Climatic and Palaeoclimatic Significance of Rock Glaciers


Leysinger Vieli, Gwendolyn, 2003. Flow Modeling of Alpine and Rock Glaciers


Mandres, Marinel. 2000. Imprints in the Landscape: Serbian Toponyms in North America . Journal of the North American Society for Serbain Studies 14(2), p 172 -200.


Ross, Clarence S., 1942. Presentation of the Roebling Medal of the Mineralogical Society of AmericaAmerican Mineralogist, v. 27, p. 155-161


Scott, Jim. 2003.  Salvage logging does more harm than goodCU News Services.


Snook, John S., 1999. The 1997 Rocky Mountain Forest Blowdown EventFSL Forum.


USGS. Surficial Geology of Mount Rainier National Park, Washington


Whalley, W.B., Azizi F., 2003. Rock Glacier Definitions. Journal of Geophysical Research, Vol 108.