Monday, September 24, 2012


 Mt. Guyot is a spectacular mountain located on the continental divide in Park County, Colorado, west of Jefferson at an elevation of 13370 ft.  The mountain may be accessed by traveling west from Jefferson on Pike National Forest Road 35 and then taking the left fork up Michigan Creek on Forest Road 54 to the summit of Georgia Pass (11,585 ft.).  The last several miles FR 54 are a high clearance, 4-wheel drive road.  Mt. Guyot is the major peak immediately west of the Pass and one can access the summit “trail” from the Pass.  However, please note that after the first quarter-mile the “trail” is a pure steep talus slope and quite moveable under human weight!

Two completely different rock units, separated by a major fault, are present in the Georgia Pass/Mt. Guyot area.  The Pass exposes outcrops of Early Proterozoic (“Precambrian”, ~1700 million years) metamorphic gneiss and amphibolite (dark colored heavy rock composed mainly of the mineral hornblende).  The Mt. Guyot massif is composed of an intrusive igneous quartz monzonite (a rock similar to granite but with significantly less quartz) of mid-Tertiary age.   It appears that the Mt. Guyot exposures are part of the much larger Bald Mountain Sill located approximately two miles to the south.  A sill is an igneous feature where the magma is intruded into previously existing rocks parallel to their bedding planes (as opposed to a dike where the magma cuts across bedding planes).    Separating these two rock units is a branch of the Elkhorn Thrust Fault (a low angle fault that has moved the older gneiss/amphibolite over the younger quartz monzonite).

There is evidence of hydrothermal alteration in the quartz monzonite and I was able to collect some really nice crystalline pyrite and chalcopyrite.  Cavities in the rock often contain micro- crystals of double terminated quartz and one specimen has fragile quartz crystals about the diameter of a “horse hair”.  One older mine was noted with a collapsed adit; however, I was unable to locate records of metallic ore production so perhaps the mine was an exploratory shaft.  Scarbrough (2001) noted the occurrence of the Horn Mine, a “uranium deposit’ in the general area of Georgia Pass/ Mt. Guyot; however, I was unable to locate the mine, or additional information.  I presume the uranium is associated with the Proterozoic rocks. 

Geologists, but perhaps few others, will recognize the name Guyot for whom the mountain was named.  In a history of geology class Arnold Guyot will always be remembered as one of the modern “fathers” of the science of glaciology.  Guyot was born in Neuchatel, Switzerland, in 1807 and graduated with a Ph.D. from the University of Berlin in 1835 (The Natural History of Lakes).  He became friends with the eminent Swiss geologist Louis Agassiz and begin studying the mountain glaciers of the European Alps, including moraines, glacier flow, and erratics.

In 1838, Guyot started a long-term project to study the geographic distribution of continental glaciers, testing the theory proposed by Agassiz that much of northern Europe had, at one time, been covered by glaciers.  He also became the first scientist to describe the differential rate of flow in an ice sheet demonstrating that such flow occurred on the molecular level.

 In 1848 Guyot immigrated to the United States and with the help of Agassiz, then at Harvard, and Joseph Henry, the Secretary of the Smithsonian Institution, begin to establish a network of weather stations in the northeast.  Eventually this network became nationwide and was the forerunner of the U.S. Weather Bureau.

 In 1854 an academic position opened at Princeton and Guyot became the first Blair Professor of Geology, a position he held for over three decades and is considered the founder of the Princeton Department of Geology.  Guyot also had a strong interest in meteorology and geography and specialized in taking barometric measurements of Appalachian peaks in order to determine their elevations.  In 1856 he established the Princeton Museum of Natural History.

Professor Guyot has been honored by the naming of three “Mt. Guyots” (New Hampshire, North Carolina, and Colorado), the Guyot Glacier in Alaska, and the Guyot Crater on the moon.  In addition, the flat-topped seamounts on many parts of the ocean floor are named “guyots”.

Arnold Guyot would have been proud of his namesake in Colorado as the mountain displays a spectacular example of a glacial cirque.  A cirque is one of the most distinguishable pieces of evidence pointing to the existence of a mountain glacier and is a semicircular bedrock feature created as glaciers scour back into the mountain. A cirque is where the snow and ice forming the glacier first accumulates.  The valley below the cirque displays the characteristic “U shape” and has several paternoster lakes (known as the Michigan Lakes).

Mt. Guyot certainly is not as famous as some of the nearby fourteeners but is a great mountain for a partial day hike, and displays some fantastic glacial landforms.  Arnold Guyot would be proud.


Scarbrough, Jr., L. Alex, 2001, Geology and Mineral Resources of Park County, Colorado: Colorado Geological Survey, Resource Series 40.

1 comment:

  1. There are actually a number of mines located on both the Park and Summit sides high on Guyot. Only a few can be entered as the rest are completely blocked by cave-in. Most cannot be readily seen or located even on the best USGS photo quads or on Google Earth. It is hard to even imagine the work miners did to achieve access to some of the mines and the history is impressive. My wife and I only wish that better records existed to document the mines and the associated history.