Wednesday, January 29, 2014


I have a soft spot in my heart for the State of South Dakota as I attended the University, completed a research project in the badlands, and have made numerous collecting trips throughout the rock column. The Black Hills are one of my favorite places to camp and explore since many of the well-exposed pegmatites are still collectable, and there are many postings on this blog detailing the geological scenery of the Hills.   However, geological features in the eastern part of the State often are overlooked; hence, the subject of this posting.

General geologic map of South Dakota.  Glacial sediments dominate East River.  West River has the Black Hills and numerous outcrops of Tertiary and Cretaceous rocks. X is Milbank, Y represents the Sioux Quartzite, Z is Glacial Lake Dakota.  Map courtesy of South Dakota Geological Survey

South Dakota exhibits a variety of landforms that the U. S. Geological Survey places into either the Great Plains or the Central Lowlands Physiographic Regions. Each of these regions is further subdivided into smaller sections.  However, I find it much easier to think of the state divisions as: 1) East River (the Central Lowlands) where the landscape is generally subdued and is covered by a variety of glacial sediments; 2) West River (the Great Plains) and its magnificent outcrops of Cretaceous and Tertiary rocks; and 3) the Black Hills, a Laramide mountain range that is part of the Great Plains but more closely related to the Rocky Mountain ranges.  Of course, the "river" here is the mighty Missouri River bisecting the state in a generally north-south direction. 

Shaded relief map of South Dakota.  Map courtesy of Ray Sterner, John Hopkins University.

For readers who have traveled east-west across the state, the changes in landscape are quite easy to observe.  East River has prairie potholes dotting the countryside and rich farm land supporting fields of soy beans and corn.  A limited number of streams exhibit rock outcrops but they are few and far between.  As soon as travelers enter West River the tilled farm lands turn to short grass cattle pastures, rock exposures are numerous, and relief becomes more noticeable. 

Prairie pothole in eastern South Dakota, probably a kettle. The retreating glacier left behind a block of ice that melted and resulted in the formation of a depression.  The water level fluctuates with ground water tables as streams neither flow into nor leave the lake.  In some years the potholes are dry.

One of the major contrasts between the two sides of the state is the arrangement of the drainage systems-consult the maps shown above.  In West River numerous streams flow in an easterly direction into the Missouri River.  Major drainage systems East River, with the exception of the James River (Jim River to local Dakotans), are rare and all flow to the south, but also empty into the Missouri.  The James heads in North Dakota, flows south in what appears on the maps to be a wide valley (the James River Lowlands), and reaches the Missouri River near Yankton.  At ~ 710 miles the James is listed by some sources as the 18th longest river (main stem) in the U.S.  Geology students at the U always were told the James is the longest unnavigable river in the states; however, that may be a rumor?  The River is quite sinuous and fits very nicely with Mark Twain’s description of another American river: It seems safe to say that it is also the crookedest river in the world, since in one part of its journey it uses up one thousand three hundred miles to cover the same ground that the crow would fly over in six hundred and seventy-five.   Gries (2009) noted that with a gradient of about an eighth of a foot per mile, water in the James takes three weeks to cross the state. 

In terms of valley width, the maps deceive viewers as the river actually flows in a fairly narrow valley that itself is located in a region known as the James River Lowlands.  This interesting feature, the Lowlands, is really the result of Pleistocene glaciation, actually at least two different glacial advances/retreats.  The first advance scoured out the Lowlands and when the second glacial advance came along it was forced down the lowland valley, squeezed between highlands to both the east and west and continued the scouring (see descriptions below).  At some time in the history of the last advance/retreat a moraine dammed the meltwater outflow from the lobe and a large lake was formed—Glacial Lake Dakota.  Sediments from this lake bed may be seen on the geologic map as the “finger’ extending down from North Dakota.  The lake finally overflowed and flooded the Lowlands creating the valley that now houses the current James River. 

The James River commonly floods in the spring season.  Notice the meandering river channel within the river valley that in turn is entrenched into the James River Lowlands.  Photo courtesy of Earth Observatory.

West of the James River is a highland area known as the Coteau de Missouri (French for Missouri Hills!).  The hills are underlain by Cretaceous bedrock but surficial rocks are mostly glacial till.  However, some small streams close to the Missouri River expose outcrops of the Pierre Shale. 
East of the James River Lowlands is a region known as the Coteau des Prairies (Prairie Hills). The escarpment leading from the Lowlands to the Coteau is one of the more noticeable areas of relief in East River (~500 feet).  The bedrock again is usually the Pierre Shale but surficial rocks are glacial till.  Dakotans know this area as “Lake Country” since prairie potholes, many times the result of ice blocks left behind (kettles), are scattered across the area.  The Coteau, along with the Missouri Hills to the west, “guided” a lobe of the Wisconsin (late Pleistocene) glacier down what is now the James River Lowland.

So, eastern South Dakota is essentially covered with glacial drift or meltwater sediments.  In a few places, notably in the southeast along the Missouri River (southern boundary) and Big Sioux River (eastern boundary), widely spaced Cretaceous rocks crop out (Pierre, Niobrara, Carlile, Dakota).  Even more interesting, however, are a couple of localities with exposures of Precambrian rocks.  On the geologic map (see above) note that in the northeast part of the state X represents the Milbank Granite.  This ~2.6 Ga rock unit sticks up above the surrounding sediments in only a few square miles along the Minnesota River.  However, numerous quarries take out large slabs of the “carnelian granite” or “mahogany granite’ (or a variety of other names) as it takes a wonderful polish.  The stone is used across the Midwest and plains (and perhaps further) for the construction of tombstones.  Milbank Granite, with its red color, is quite easy to identify in cemeteries. As a small side note, companies that commercially market tombstones are great places for field trips as they have a variety of well-displayed igneous and sometimes metamorphic rocks.

Polished “mahogany granite” quarried from near Milbank, South Dakota.  Photo courtesy of Fisher Monuments.

The Milbank granite “sticks up” in an area called the Minnesota River Lowlands that is home to a really interesting area called Browns Valley.  This Valley holds Lake Traverse whose waters flow north via the Red River into Hudson Bay.  The Lake is separated at the south end by a feature named the Traverse Gap from Big Stone Lake whose waters flow southeast into the Mississippi River.  Therefore, Traverse Gap is a continental Divide, albeit not one that Coloradoans might recognize!
 Lake Agassiz was a major (~110,000 mi2) late Pleistocene lake situated in North Dakota, Minnesota and Canada resulting from melting waters of the large continental glacier (Wisconsin: Laurentide Ice Sheet).  About 9700 years ago these meltwaters broke through a glacial moraine (debris piled up by an advancing glacier) creating Traverse Gap while flooding southeast in a valley now known as Glacial River Warren.  This was a “major” flood and created the extra-large valley now occupied by a “small” Minnesota River.

Aerial view of Traverse Gap looking south from Lake Traverse toward Big Stone Lake. Minnesota is on the left side, South Dakota on the right.  This shot was taken during a spring flood and water is over the Continental Divide (brown water covering Traverse Gap.  Will the flood water flow into the Mississippi River, or to Hudson Bay?  Photo courtesy of JOR Engineering, Inc.

The second area of interest is around and in the city of Sioux Falls (and in neighboring Iowa, Minnesota) where exposures (sticking up through the glacial drift) of a hard and scenic pink quartzite dot the countryside—see Y on the map.  The Precambrian (Proterozoic, ~1.75 to 1.65 Ga) Sioux Quartzite is, as the USGS describes, a “pink, reddish to tan, siliceous, fine to coarse-grained, iron-stained orthoquartzite with minor conglomerate and mudstone layers.  Estimated thickness is greater than 1,000 ft.”  Orthoquartzite is not a metamorphic quartzite but tightly cemented quartz arenite (sandstone).  The quartzite most likely was deposited by braided streams flowing into an old Precambrian ocean.  It is quarried at many places and numerous buildings in Sioux Falls and other cities/towns are constructed of the rock as well as tens of miles of “rip-rap” the Corps of Engineers has placed along the Missouri River and other streams.  I have examined many miles of this rip-rap (while searching for walleye) and cross-bedding and ripple marks are common features.

Fig. 8.  Sioux Quartzite exposed at the “falls” in the city of Sioux Falls.  Photo courtesy of Steve Dutch, University of Wisconsin.

The Missouri River Trench is a major topographic and geologic structure trending mainly north-south in the center of the state until the river abruptly turns east and then forms the boundary with Nebraska (the informal South Dakota boundary between “East River” and “West River”).   The Cretaceous Pierre Shale is well exposed along the entire trench, and in many places the underlying Niobrara Formation crops out.  In fact, the type section (where it was named) of the Niobrara is along the bluffs west of Yankton along the Niobrara River where it meets the Missouri River.  The Pierre Shale was named for exposures near the South Dakota state capitol, the city of Pierre, also situated along the Missouri.  Many readers are familiar with these two formations if they have traveled along I-90 and crossed the river at Chamberlain.  The view of the river and the Trench rocks is spectacular, especially if traveling from east to west. A long time ago I spent a summer in Chamberlain trying to unravel the secrets of landslides in the Pierre in preparation for the construction of I-90. 
I wish to thank Ray Sterner of the John Hopkins University Applied Physics Laboratory for allowing me access to his files of state relief maps.

For additional information about other geological aspects of eastern South Dakota, see

8/13/13: Wow-South Dakota Artesian Well
8/19/13:  South Dakota Lake Superior Agate
6/7/11: Mining for Manganese

Gries, J. P., 1996, 2009, Roadside Geology of South Dakota: Missoula, Mountain Press Publishing Company.

Wednesday, January 22, 2014


Make choices based not on fear, but what really gives you a sense of fulfillment.  P. R. Chance

A long time ago, in human years and not geologic time, I managed to graduate from a small, really small (48 total students in school) high school in central Kansas.  As a first generation college student I headed off to school without the slightest idea about any sort of a career choice.  My knowledge about higher education consisted of wanting to play basketball as that activity paid the way for classes.  I sort of failed at both aspects as the court was full of much better players and my grades were not the best.  So, I decided to declare a major, engineering, to better define my goals (and hopefully my grades).  I was soon out of that field since my skills with a slide rule were pretty meager (hopefully some of the readers might remember these mechanical analog computers).  Next came chemistry; however, my only skill in that major was setting records for broken glassware (it cost me a fortune).  One day as a second year student, I “had” passed the first year, I was sitting around reading the college catalog and trying to figure out the rest of my life—when I came across “the geology major”.  An epiphany was in progress since my mind wandered back to childhood days of collecting rocks and minerals and I marched over to the department and declared a new major!  Wow, just like that I had a new meaning in life and I have never looked back.
So, how does my childhood relate to azurite and blueberries?  Well, one of the joys of being a geologist is “going to the field”, a term I have used several times before in these writings. Many years ago I was working with a paleontologist, in the field, chasing phytosaurs (crocodile-like animals) out near Bedrock, Colorado (far western part of the state).  Part of the group decided to wander, on the way home, over to the La Sal Mountains where there was an old copper mine.  And, that is how I was introduced to azurite. 
Cartoon showing an idealized laccolith intruding into sedimentary rocks. 
The La Sal Mountains are just across the Utah—Colorado state line near Moab, Utah.  They are part of a group of scattered and isolated mountain chains known as the laccolithic centers of the Colorado Plateau.  Laccoliths are igneous intrusions that have been injected into layers of sedimentary rocks and have pushed up the overlying rocks into a dome. The name, laccolite, was first coined by one of the most famous geologists in the annals of the U. S. Geological Survey (USGS), Grove Karl Gilbert in his monograph (1877), Report on the Geology of the Henry Mountains.  At the time Gilbert was working for the “Powell Survey”, one of the early USGS surveys designed to study the geology of the “American West”, and Gilbert was assigned to map the Henry Mountains, the last major mountain range to be “discovered” in the lower 48 states.  Gilbert noted in the Monograph introduction that the Henry Mountains have been visited only by the explorer.  Previous to 1869 they were not placed upon any map, nor was any mention made of them…  Gilbert also believed these island mountains were different, not really a chain, and maybe just a group of five individual mountains (Mts. Ellen at 11,522 feet, Pennell, Holmes, Hillers, and Ellsworth).  Furthermore, he stated that instead of rising [the magma] through all the beds of the earth’s crust it stopped at a lower horizon, insinuating itself between two strata, and opened for itself a chamber by lifting all the superior (overlying) beds.  Gilbert called this type of igneous formation a laccolite, currently known as a laccolith. Today, erosion has stripped off the overlying sedimentary rocks and the core diorite (dark gray igneous rock with large amounts of plagioclase feldspar; emplaced ~20--29 Ma; Sullivan, 1997) core is exposed with the tilted sedimentary rocks cropping out on the mountain flanks.  As in Gilbert’s Day, the Henry Mountains are still one of the most isolated ranges in the lower 48 states.
Location map of mountain ranges associated with laccolithic centers in the Colorado Plateau.  The Four Corners is represented by the red dot.  L, la Sal Mountains; A, Abajo or Blue Mountains; S, Ute Mountains; C, Carrizo Mountains; H, Henry Mountains; N, Navajo Mountains.  Photo from National Aeronautics and Space Administration Visible Earth Project.
After Gilbert’s work geologists then begin to describe other laccolithic centers in the Colorado Plateau.—the La Sal, Abajo, Carrizo, Ute Mountains, Navajo Mountain, Ophir-San Miguel-Klondike Ridge (Mutschler and others, 1997).  All of these laccoliths have the igneous rocks exposed in the center with the exception of Navajo Mountain on the Utah-Arizona state line.  At that locality, which is a single domed peak (10,388feet), the overlying sedimentary rocks have not been eroded away to expose the underlying igneous rocks.
Navajo Mountain with part of Lake Powell in the foreground.  Public Domain photo courtesy of G. Thomas.
I might add, at this point, that not all laccoliths are large mountains and not all are located in the Colorado Plateau.  For example, Tomichi Dome west of Gunnison, Colorado, is a laccolithic dome with igneous magma intruded into the Dakota Sandstone and the Mancos Shale.  Although the elevation is substantial (11,471 feet), the hill is much smaller in size than the large centers in the Colorado Plateau.
Tomichi Dome, a Tertiary laccolith located in Gunnison County about 20 miles east of Gunnison, Colorado.  The dome is situated just south of Waunita Hot Springs and their water temperature may be related to the heat of this igneous intrusion. 
The grandest laccolithic center of the Colorado Plateau is the La Sal Mountains near Moab, Utah.  Mt. Peale at 12,721 feet is the highest of this large group of peaks although 11 other peaks have elevations in excess of 12,000 feet.  The mountains are impressive and can be seen from tens of miles distance. The magma, now the rocks diorite and rhyolite, was emplaced around ~28-29 Ma (Sullivan, 1997).  The peaks are especially scenic when viewed from Arches National Park to the north.
La Sal Mountains as seen from Arches National Park.

Immediately to the south of the La Sal Mountains is Lisbon Valley containing the Lisbon Valley Anticline, a large salt anticline where the dipping beds are due to movement/solution of salt in the subsurface.  Several of these salt structures are found in the greater Paradox Basin (an evaporate basin in Utah and Colorado near the Four Corners).  Although the Valley has several tens of producing gas wells, the most active mineral commodity has been the numerous uranium mines (earliest report in 1913) and the area is undergoing uranium resurgence today.  Target zones have been, and still are, the Cutler Formation/Group (Permian), the Moss Back Member of the Chinle Formation (Triassic), and the Salt Wash Member of the Morrison Formation (Jurassic) found along the flanks of the anticline. 
Copper also is present in varying quantities and qualities in Lisbon Valley and has been periodically mined for decades.  Most of the paying copper deposits seem to be in the Dakota Sandstone and Burro Canyon Formation, both Cretaceous in age---therefore younger and above the uranium beds.  Most of the copper ore is chalcocite (Cu2S) deposited by solutions brought up along the Lisbon Valley Fault (found along the crest of the anticline with offset approaching 4000 feet).  With time chalcocite oxidizes to such secondary minerals as azurite [Cu3(CO3)2(OH)2] and malachite [Cu2(CO3)2(OH)2], both copper carbonates, (but note that azurite commonly pseudomorphs to malachite), and tenorite [CuO] and cuprite [Cu2O], both copper oxides (SRK Consulting, 2006).
Satellite image, oblique view, of Lisbon Valley looking northwest down the strike of the Lisbon Valley Anticline.  Photo courtesy of Mesa Uranium Corporation.
One of the earliest mining areas in the Lisbon Valley/La Sal District was originally organized in 1892 and generally goes under the name of Big Indian Copper Mine with later mines and claims termed Blue Jay Claim, Blue Grotto Prospect, Nevada Claim, Blue Crystal Mine, and the Texas Claim.  A copper processing mill was constructed in 1918 and mining continued sporadically for several decades.  The ore body is comprised of oxidized copper minerals (see above) emplaced in the Cretaceous Dakota Sandstone along the downthrown side of the Lisbon Valley Fault; mining has been via open pit and tunnels.  In the late 1970’s prospectors begin to notice beautiful azurite crystals and specimen collecting went into operation.  For example, in 1988 a cut on the Nevada Claim produced one hundred thousand specimens of azurite rosettes (for collectors) and 6000 pounds of broken nodules for paint pigment.  Today the claims are generally referred to as the Blue Crystal Mines and the company offers mineral collecting on a fee basis through tours arranged by Rockpick Legend Company in Salt Lake City and Deep Desert Expeditions in Moab.  

Besides the abundance of azurite, other minerals collected from the claims and mines include: Wulfenite, Tyrolite, Tenorite, Tennantite, Sphalerite, Quartz, Pyrite, “psilomelane”, Olivenite, Malachite, Kaolinite, Goethite, Enargite, Djurleite, Diginite, Cuprite, Covellite, Cornwallite, Copper, Conichalcite, Clinoclase, Chrysocolla, Chalcopyrite, Chalcopyrite, Chalcophyllite, Chalcocite, and Calcite.  Information in this paragraph came from an article by Arnold G. Hampson (1993).

During my little expedition in the latest 1970’s (maybe earliest1980’s??) I was able to collect numerous representatives of copper minerals; however, after several house moves and “give-aways”—I have three remaining specimens.  Fortunately I was able to keep one cluster or rosette and one “blueberry” of azurite and one small mass of malachite. The most unique of the specimens collected at the Blue Crystal Mine, then and now, are the “blueberries”, small (up to 5mm) concretions, often hollow, of microsized azurite crystals; some contain tiny rounded quartz grains mixed with azurite.  I have not been able to locate information on their formation; however, it appears that tens of thousands of these “blueberries” have been collected over the decades.  Rockhounds in Utah tell me that the mine is the single world source for these unique specimens; however, I have seen similar/almost identical specimens from the El Chino Mine in New Mexico.
The “azure colored” rosettes and crystal clusters “commonly occur as 3-8 cm rosettes of subparallel crystals and as individual crystals to 2.5 cm in length” (Hampson, 1993).  The blueberries are much lighter in color, perhaps a sky blue.   
Azurite crystal cluster bottom (3 x 2.6 cm) from Blue Grotto Prospect, La Sal/Lisbon Valley District.  Photo courtesy of Kevin Conroy.  Azurite blueberries, top.  Photo courtesy of Blue Crystal Mine.
 Azurite has been used as a dye and/or paint pigment for centuries; hence, several thousand pounds from the Big Indian area being shipped to Japan (see above).   At a hardness of 3.5 -4.0 (Mohs) azurite is somewhat too soft for certain jewelry pieces such as rings.  However, I have seen nice stones in pendants but the wearer must use extreme caution against “banging it around”.  Some Native American cultures regard azurite as sacred.  In my opinion, since azurite is such a stunning mineral the best use is as a specimen in the collecting case!  However, I have noticed that some spiritualists believe azurite may be used to expand the mind, fortify the memory, and clear stress---now that is a real stone for the baby boomers and I may go into business stimulating memories. 
So, that is the story of how a bunch of broken chemistry glassware led a directionless and drifting young man to collect azurite blueberries in a Colorado Plateau laccolithic center.

It was my good fortune in 1935 to be assigned chief of a U.S. Geological Survey field party studying and mapping the geology of the Henry Mountains, Utah. Geologically the area is of great interest because of the classic work done there in 1876 by G.K. Gilbert for the Powell Survey. In the 1930’s the area still was frontier—a long distance from railroads, paved roads, telephones, stores, or medical services. It was the heart of an area the size of New York State without a railroad, and a third of that area was without any kind of a road. This was not Marlboro country; it was Bull Durham country. The geological work had to be done by pack train; it was about the last of the big packtrain surveys in the West—the end of an era.  Charles B. Hunt

SRK Consulting, 2006, Constellation Copper Corporation: Resource Estimate Centennial Deposit: private report. 

Hampson, A. G., 1993, Minerals of the Big Indian Copper Mine San Juan County, Utah: Rocks and Minerals, v. 68, No. 6.

Mutschler, F. E., E.E. Larson, and M. L. Ross, 1997, Potential for Alkaline Igneous Rock-Related Gold Deposits in the Colorado Plateau Laccolithic Centers in Friedman, J. D. and A. C. Huffman (Coordinators), Laccolith Complexes of Southeastern Utah: Time of Emplacement and Tectonic Setting—Workshop Proceedings: U. S. Geological Survey Bulletin 2158.
Sullivan, K. R. 1997, Isotopic Ages of Igneous Intrusions in Southeastern Utah in Friedman, J. D. and A. C. Huffman (Coordinators), Laccolith Complexes of Southeastern Utah: Time of Emplacement and Tectonic Setting—Workshop Proceedings: U. S. Geological Survey Bulletin 2158.