CALCITE FROM LA GARITA

The San Juan Mountains are known to most geologists as a volcanic terrane since there is a tremendous amount of evidence pointing to numerous volcanic eruptions in the Tertiary (last 66 million years or so). The San Juan’s are also home to perhaps 60 volcanic calderas, usually circular or oblong collapse features indicating ancient volcanoes that “blew their stack”.  The largest of these features is known as the La Garita Caldera, a truly gigantic structure.  Ort (1997) estimates the caldera was approximately 22 X 45 miles in size and produced about 5000 cubic-miles of volcanic material.  The pyroclastic ejecta generally are referred to the Fish Canyon Tuff (a silica-rich quartz latite containing about 40 per cent phenocrysts) that was scattered over a wide area with wind-blown ash perhaps reaching the east coast of the U. S.  There is a radiometric date of 27.8 Ma (Tertiary: Oligocene) on the rock unit (Ort, 1997).

 THE SAN JUAN VOLCANIC FIELD.  MAP FROM BACHMANN AND OTHERS, 2002.

The eruption of the La Garita Caldera is related to the Mid-Tertiary Ignimbrite Flare-Up, a period of very explosive volcanism centered in Nevada, Utah and Colorado approximately 25-40 Ma (Cannon, 2002).  In fact, the San Juan Mountains are the result of several of these volcanic explosions producing both lava rock (basalt) and pyroclastic rocks like ash and tuff.

 

  FISH CANYON TUFF, SAGUACHE COUNTY, COLORADO.

Since the initial blowout of the Fish Canyon Tuff, Carter (2009) has described seven additional eruptions seemly clustered near the center of the La Garita Caldera.  One of these eruptions created the Bachelor Caldera and spewed out the 190 cubic-mile Carpenter Ridge Tuff.  About 27 Ma an explosion created the San Luis Caldera and ejected the 135 cubic-mile Nelson Mountain Tuff.  At 26 Ma the same volcano created the Creede Caldera that expelled the 120 cubic-mile Snowshoe Mountain Tuff.

The Crystal Hill Mining District is located a few miles north and west of the community of La Garita near Carnero Creek.  The District was founded in 1881 by prospector and mining man Mark Biedell.  Crystal Hill produced native gold and silver from a collapse breccia structure for a few years before mining operations ceased, mostly by 1900.  Two small, short-lived mining camps sprang up in the area. The first, Biedell, appeared in 1881 and 1000 men were mining by 1883; the second sprang up in 1886 and was known as El Carnero (GeoZone, 2011).  The latter area was producing from “lead carbonate” (BLM information sign), a mineral I presume is cerussite (PbCO₃).  Eckel (1997) did not mention cerussite at Crystal Hill but did note its occurrence at the Bonanza District about 30 miles away: “…cerussite followed angelesite and covellite as shells on massive galena.”  

In the 1940’s mining evidently returned to Crystal Hill in the form of the Crystal Hill Mining Company (BLM information sign); however, I was unable to locate additional information about this later activity.

Voynick (1994) noted that “exploration geologists returned to Crystal Hill in the late 1970’s, delineating a large, low-grade zone of disseminated gold near the top of the hill.  The Crystal Hill Mining Company developed an open-cut heap leach mine recovering 30,000 troy ounces of gold in four years”.  In 2009?  U. S. government “stimulus funding” allowed the BLM to reclaim, at least partially, the old mine.  BLM now allows access on the reclaimed area but warns that the main pit is off limits and is situated on private land. 

   SLENDER TERMINATED QUARTZ CRYSTALS FROM THE CRYSTAL HILL MINE. WIDTH ~ 4.2 CM.

The Crystal Hill Mine is best known for producing terminated quartz and amethyst crystals and I wrote about these specimens in a posting on November 19, 2011.  However, another interesting specimen mineral coming from Crystal Hill is aragonite/calcite.  Voynick (1994) described the crystallization process as: “The last solution [a high-silica solution] which leached downward from the surface carried calcium carbonate from dissolved limestone.  The silica crystallized as drusy quartz and, in vugs, as well developed crystals of clear, smoky, and amethyst quartz crystals…  The dissolved limestone recrystallized as white needles of drusy calcite.”

 

  CALCITE CRYSTALS OVERLAIN BY GLOBULAR ARAGONITE. WIDTH ~ 5 CM.

My Crystal Hill specimen has scalenohedron calcite crystals overlain by rounded aragonite and is quite impressive.  John Betts (John Betts Fine Minerals) states that the aragonite fluoresces green and the calcite fluoresces blue-white under UV illumination.  However, I have neither a short-wave nor long-wave lamp to check this statement.

REFERENCES CITED

Cannon, E., 2002, The Mid-Tertiary Ignimbrite Flare-Up: www.colorado.edu/GeolSci/Resources/WUSTectonics/CzIgnimbrite/ignimbrite_intro.html.

Carter, J., 2009, La Garita: the World’s Largest Eruption: AssociatedContent,  www.associatedcontent.com/article/1001330.

Eckel, E. B., and others, 1997, Minerals of Colorado: Golden, Fulcrum Publishing.

GeoZone, 2011, The Lost Mine of Saguache Creek:
www.thegeozone.com/treasure/colorado/tales/co014b.jsp#prospecting

Ort M., 1997, New Results for the 27.8 Ma Fish Canyon Tuff and the La Garita Caldera, San Juan Volcanic Field, Colorado: Commission on Explosive Volcanism,
http://staff.aist.go.jp/s-takarada/CEV/newsletter/lagarita.html

 Voynick, S. M., 1994, Colorado Rockhounding: Missoula, Mountain Press Publishing Company.

MT. GUYOT

MOUNT GUYOT, PARK COUNTY, COLORADO.

 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”.

BACK WALL OF CIRQUE.

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).

LOOKING DOWN GLACIAL VALLEY AT 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.

SUMMIT OF MT. GUYOT.

REFERENCES CITED

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

JELINITE (AMBER): THE HOLY GRAIL OF KANSAS MINERALS

JELINITE, AMBER, FROM ELLSWORTH COUNTY, KANSAS, KIOWA FORMATION (CRETACEOUS).  COLLECTION OF GLENN ROCKERS.

 I was able to attend the recent 45^th Annual Denver Gem and Mineral Show and found the exhibited specimens quite beautiful.  The Show theme this year was “Copper and Copper Minerals” and varieties of copper-bearing minerals, as well as large hunks of native copper, were spectacularly displayed.  I spent a large amount of time sort of staring into the cases wondering why I could never find such specimens!  I also made the rounds of several dealers and was able to visit with one of my heroes, Bob Jones, the Senior Editor of Rock and Gem Magazine. But, my highlight of the entire Show was getting to see the Holy Grail of Kansas Minerals!

Surficial rocks in Kansas are almost entirely sedimentary—lots of limestones, shales, and sandstones.  Many are quite fossiliferous and excellent collecting opportunities exist for invertebrates of Pennsylvanian, Permian and Cretaceous ages.  However, collectors of specimen minerals often bypass the state.  Mississippian rocks in extreme southeastern Kansas, part of the Tri-State Lead and Zinc District, have produced very nice specimens of galena, dolomite, chalcopyrite, and sphalerite.  Late Paleozoic rocks give up a few geodes with calcite and occasionally celestine.  Cretaceous rocks yield some marcasite and pyrite while the Tertiary and Pleistocene sediments offer numerous types of microcrystalline quartz.  Some outcrops of the Tertiary Ogallala Group have yielded non-gemmy moss opal.  But, generally speaking, Kansas minerals are not “rare” and crystal collectors often head to the east to the Ozarks and Ouachitas, west to Colorado, or north to the Black Hills.

But, there is one Kansas mineral that is quite rare with essentially all of the very few collected specimens coming from a single small locality that is no longer accessible and is now located under several tens of feet of water in a Corps of Engineers reservoir.  That is why I have termed jelinite the Holy Grail of Kansas Minerals!

Jelinite, first described as kansasnite, is actually a type of amber and is a local name honoring the initial collector, George Jelinek, who found the first specimens in 1937-38 along the Smoky Hill River in Ellsworth County, Kansas (Buddhue, 1939a; 1939b).  The amber came from a “layer of soft sulfur-colored clay bounded by two thin lignite layers” (Langenheim and others, 1965).  There was some debate about the exact geological formation that produced the amber and originally specimens were ascribed to the Cretaceous Dakota Formation since this unit contains many more lignite beds than the underlying Kiowa Formation. 

The confusion about the stratigraphic units seems reasonable (at least to me) since at many outcrops in Ellsworth County (and other localities) the rocks appear similar and are difficult to distinguish between.  Bayne and others (1971) noted that: both formations are heterogeneous units of shale, sandstone, and siltstone with pyrite, marcasite, gypsum crystals, ironstone concretions, and lignitized wood fragments. The mostly non-marine Dakota Formation was deposited during the retreat of the Kiowa Sea in a bordering low-lying coastal or deltaic plain.  The underlying Kiowa Formation was deposited in nearshore to coastal environments as the early Cretaceous sea spread northeastward across gentle terrain developed mainly on Permian rocks.  So, the Dakota has sparse nonmarine fossils (such as leaves) in Ellsworth County outcrops while the Kiowa has a few marine gastropods and mollusks.  But, both units have tightly cemented “quartzite” (CaCO₃) lenses (an interesting issue).  It is easy for roadside travelers to confuse the two units without the presence of fossils or a good geologic map. 

 

Both formations have beds of lignite although such beds are thicker and more numerous in the Dakota.  However, detailed mapping of the stratigraphy near Kanopolis Reservoir led Bayne and others (1971) to state “the fossil amber (jelinite) found in the NW SW sec. 18, T. 17 S., R. 6 W. …probably came from such a sequence [carbonaceous clay] in the lower parts of the Kiowa Formation.”  This was a confirmation of previous statements by Langenheim and others (1965).

So, the amber did originate in the Kiowa Formation.  However, with the construction and filling of Kanopolis Reservoir in 1948-1951 covering the collecting locality, any refinement of stratigraphy is destined for the far future.

Schowe (1942) examined specimens of jelinite and described them as "light butterscotch in color or some other shade of brown. It is waxy, shines as if polished, is cloudy to translucent, and is made up of more or less concentric bands somewhat like agate. The amber has a hardness of about 3... It is brittle and breaks with a conchoidal or shell-like fracture.”

Although macrofossils seem absent from the jelinite, Waggoner (1996) reported the presence of sheathed bacteria, amoebae and other microfossils.  The presence of succinic acid (C₄H₆O₄) in jelinite led Buddhue (1938) to suggest a conifer origin for the amber.  Langenheim (1969) noted that almost all Cretaceous ambers from North America came from members of the Araucariaceae (a conifer).

I want to thank Glenn Rockers of Paleosearch Inc., Hays, Kansas, for showing me his specimen, letting me hold the Holy Grail, and for allowing photographs.  Glenn informed me the specimen in his possession was purchased by an unnamed person at an estate auction and was part of the original Jelinek collection.  He also stated there is a much larger specimen floating around in a private collection.  Now, if I could only find an estate auction like that! 

  

REFERENCES CITED

Bayne, C. K., P. C. Franks, and W. Ives, Jr., 1971, Geology and Ground Water Resources of Ellsworth County, Central Kansas: Kansas Geological Survey Bulletin 201.

Buddhue, J. D., 1938a, Some New Carbon Minerals—Kansasite Described: The Mineralogist, v. 6, no. 1. 

Buddhue, J. D., 1938b, Jelinite and Associated Minerals: The Mineralogist, v. 6, no. 9. 

Langenheim, J. H. 1969, Amber-a Botanical Inquiry: Science v. 16, no 3.

Langenheim, Jr., R. L., J. D. Buddhue, and G. Jelinek, 1965, Age and Occurrence of the Fossil Resins Bacalite, Kansasite, and Jelinite: Journal of Paleontology v. 39, no. 2.

Schoewe, W. H. 1942. Kansas Amber: Kansas State Academy of Science, Transactions no. 45.

Waggoner, B. M. 1996, Bacteria and Protists from Middle Cretaceous Amber of Ellsworth County, Kansas: PaleoBios v. 17, no.1.

mike

ARIZONA GLAUBERITE PSEUDOMORPHS

CALCITE PSEUDOMORPH AFTER GLAUBERITE.  LENGTH ~5 CM.

 One of the more interesting groups of minerals are the pseudomorphs, or false form minerals--essentially a new mineral recrystallizes and replaces the original mineral.  During this chemical change the replacing mineral takes on the crystal form of the original mineral and that crystal form commonly is atypical for that particular replacing mineral!  That is, the shape of the original mineral is maintained by the replacing mineral. 

For example, both azurite and malachite are quite recognizable copper minerals with azurite being blue in color while malachite is a bright green.  Both minerals are copper carbonates with azurite (Cu₃(CO₃)₂(OH)₂)) crystallizing usually as prismatic crystals while malachite (Cu₂CO₃(OH)₂) crystals are often slender prisms.  Azurite is unstable and with weathering some of the carbon dioxide (CO₂) chemically changes into water and the +++copper cation becomes ++copper cation.  This seems a fairly complex chemical change for such beautiful minerals!

Near Lake George in the pegmatites of the Pikes Peak Batholith, hematite is a pseudomorph after siderite.  Hematite is an iron oxide (Fe₂O₃) and often a weathering product, in this case of siderite, an iron carbonate (FeCO₃) with a rhombohedral form.

At many rock and mineral shows vendors will display glauberite pseudomorphs that were collected from near Camp Verde, Arizona, north of Phoenix.  At this locality exposures of the Verde Formation are well-exposed in an abandoned salt mine.  The Verde was deposited in a large lake that occupied a tectonic basin in central Arizona during the Pliocene and Pleistocene epochs, approximately two to eight million years ago (Ayres, 2009).  Near the end of the lake cycle the water became quite saline and evaporitic minerals such as halite (sodium chloride-- NaCl) and glauberite (sodium calcium sulfate-- Na₂Ca(SO₄)₂ were deposited.

THE "SALT MINE" NEAR VERDE, ARIZONA.

 I am uncertain about the chemistry but sometime in the last two million years carbonates, calcite (CaCO₃) and/or aragonite (CaCO₃), or a sulfate, gypsum (CaSO₄-2(H₂O)), replaced the unstable glauberite as a pseudomorph.  I presume that groundwater percolating through the sediments and rocks provided the appropriate replacing elements.

GYPSUM PSEUDOMORPH AFTER GLAUBERITE.  LENGTH ~10 CM.

  I also recognize there is a name similarity between glauberite and Glauber’s salt, the latter being a sodium sulfate decahydrate (Na₂SO₄-10H₂O), for which the mineral was named.  In past years some glauberite was mined to produce Glauber’s salt, a substance used in the chemical industry.  Glauberite itself is mostly colorless to cream to gray in color, rather soft at 2.5 on the Moh’s Scale, and has a white streak.  Glauberite is impressive due to the unmistakable, large, well-formed, tabular- to wedge-shaped crystals that define the mineral.  This characteristic shape seems enough to distinguish the mineral from others.  However, as noted above, there is a problem--glauberite is unstable and often is replaced by other minerals producing pseudomorphs and these “false form minerals” seem more common in the record than true glauberite crystals! 

In my collecting at the salt mine I was able to secure: 1) a beautiful large specimen of several crystals of gypsum that were pseudomorphs of glauberite, and a “typical” crystal of calcite pseudomorph after glauberite.  I also collected a transparent and non-crystal specimen that an Arizona geologist identified as thenardite (a mineral that was unfamiliar to me).  Thenardite is a sodium sulfate, Na₂SO₄, that also precipitates in evaporitic lakes and playas.  Interesting, but perhaps confusing to non-geochemists, are the facts that thenardite: 1) is the salt of sulfuric acid; and 2) and becomes Glauber’s salt with the addition of water!

A couple of other interesting comments about glauberite might be in order.  In New South Wales, Australia, opal (SiO₂-nH₂O) is found as a pseudomorph after glauberite.  At Watchung, New Jersey, both prehnite (a calcium, aluminum phyllosilicate, Ca₂Al(AlSi₃O₁₀)(OH)₂)) and quartz (SiO₂) occur as pseudomorphs after glauberite in basalt cavities.

I am somewhat out of my realm of comfort here since I am not a mineralogist or geochemist and do not fully understand some of the processes taking place during the formation of pseudomorphs.  However, the glauberite pseudomorphs are quite interesting and make excellent display specimens.  For additional information on the Camp Verde specimens please see Ayres (2009) or Thompson (1983).

REFERENCES CITED

Ayres, S., 2009, The Verde Formation: A Story That Holds Water: Verde Independent (newspaper), November 18, 2009. 

Thompson J. R., 1983, Camp Verde Evaporates:  Mineralogical Record, Vol. 14 No. 2, p. 85-90.

PETRIFIED WOOD: WHAT ARE THE STRUCTURES?

UPPER (TOP) OF A PARTIAL LOG REPLACED BY MICROCRYSTALLINE QUARTZ (PETRIFIED WOOD) WITH VARIOUS INTRUDING STRUCTURES.  ARE THESE TUBES PRIMARY OR SECONDARY?  

 In a blog on August 11, I reported on the existence of a quite large piece of mammillary chalcedony observed during a trip to South Park Basin, Colorado.  The blog also contained information about the geology/formation of the Park so that will not be repeated here.

The northern part of the Park (north of US 24) has numerous mountain ranges in the east such as the Kenosha and Tarryall Mountains where the bed rock is generally Precambrian in age.  On the western flank rocks of Paleozoic age front the Mosquito Range.  South of the highway the landforms are more subdued and a wide variety of Cenozoic, volcanic-related rocks overlie Mesozoic bedrock; however, the Mesozoic rocks often crop out in north northwest trending ridges (easily seen near Hartsel and extending north) (Scarbrough, 2001 ).  My interest, in various collecting trips to South Park, has generally been in the southwestern part of the Basin where Scarbrough (2001) has outlined the Cenozoic history as follows:

Deposition of Denver (South Park?) Formation concurrent with Laramide tectonism (compressional mountain and basin building) in the early Tertiary.

Middle Tertiary erosion, then deposition of lake beds, volcanism in the form of lavas and extensive airfall deposits, igneous intrusions, and fluvial deposits.

Pleistocene glaciation in the adjacent mountains producing outwash deposits.

Deposition associated with Holocene fluvial systems.

One of the best-known volcanic-associated units is a formation usually mapped as the Florissant Lake Beds. These beds crop out near Lake George and represent deposition is a basin partially occupied by a late Oligocene Lake.  Thousands of fossil plants and insects (and various other vertebrates and invertebrates) have been extracted from these beds and have produced a wonderful snapshot of life during this time period.  Today, Florissant Fossil Beds National Monument preserves several of the outcrops.

Heading south from Hartsel on CO 9 and 53 Rd, the Antero Formation of Oligocene age (probably equivalent to Florissant Lake Beds) crops out.  However, good exposures are somewhat rare since the rocks are highly weathered at the surface; the landscape is a gently rolling surface.  But, a little prospecting and walking will likely produce specimens of petrified wood.  In fact, I was able to even locate wood in ditches along a gravel road.  However, a word of caution---the land ownership situation in South Park is a jumble of Colorado State land, BLM land, and private land.  In fact, a representative from a federal agency told me that the only way for a novice (like me) to determine land ownership was to take my GPS, get a latitude and longitude reading, and compare such with a federal data base.  An easier way is probably to visit with the ranchers and request permission to prospect.

The Antero Formation is a clastic and volcaniclastic unit that contains water-laid ash, air-fall tuff, siltstone, sandstone, and algal limestone and …contains fossil plants, insects, mollusks, and vertebrates (Epis and others, 1979; Scarbrough, 2001).   A number of writers have noted the presence of petrified wood in South Park, perhaps beginning with Orvando Hollister in 1867:  This Park has salt springs, beds of gypsum, coal shales, veins of chalcedony, carnelian, and other curious stones and minerals.  It has not been thoroughly explored and no one fully knows its resources or curiosities.  Silicified wood abounds in its lower portion, and at one point, about 30 miles west of Pike’s Peak, there is a small patch of petrified stumps still standing, one of which is fifteen feet in diameter [now Florissant Fossil Beds National Monument].

Although I saw much wood in the area, one particular partial log really attracted my attention, mainly for its seemingly internal structures—as seen on the photo.  I don’t know what these structures represent but could guess they might be some sort of activities related to insects.  I am hoping that someone in cyber world will notice these structures and help me out! 

A more detailed account of South Park geology, and the petrified wood and chalcedony, will appear in the CSMS Pick & Pack (probably September) 

REFERENCES CITED

Epis, R.C., Wobus, R.A., and Scott, G.R., 1979, Geologic Map of the Guffey Quadrangle: U.S. Geological Survey Miscellaneous Investigations Map I-1180.

Hollister, O. J., 1867, The Mines of Colorado: Samuel Bowles & Company, Springfield, MA. reprinted 1974, Promontory Press, New York.

Scarbrough, Jr., L. A., geology and Mineral Resources of Park County, Colorado: Colorado Geological Survey Resource Series 40.

Wallace, C. A., J. A. Cappa and A.D. Lawson, 1999, Geologic Map of the Gribbles Park Quadrangle, Park and Fremont Counties, Colorado:  Colorado Geological Survey Open-File Report 99-3 (with map).