Spanish Diggings Orthoquartzite

Figure One - Colby-variety Clovis point on the left and Hell Gap point on the right, both 
surface-recovered approximately thirty miles west-northwest of Spanish Diggings. I 
believe the raw material for both points is Spanish Diggings orthoquartzite. 
John Bradford Branney Collection.      

The Spanish Diggings prehistoric rock quarries lie on the northwest flank of the Hartville Uplift in eastern Wyoming. The Hartville Uplift is an elongated, north-northeast trending structural arch that is twenty-five miles wide and forty miles long and ranges in elevation from 4,700 to 6,100 feet above sea level (figure two). The Hartville Uplift was created during the Laramide Orogeny in the late Cretaceous around fifty to seventy million years ago. The Laramide Orogeny was a geological event of grand importance and involved intense mountain building and structural basin creation in western North America from Canada through the United States and into east-central Mexico.  

Figure Two - Google map of eastern Wyoming looking to the northwest. The Hartville Uplift 
is marked and the location of Spanish Diggings is circled in orange. PRB and DB in black 
are Powder River Basin and Denver Basin, respectively. Photo courtesy of geowyo.com.   

For archaeologists and artifact collectors, the Hartville Uplift is known for its quality cherts and orthoquartzites coming from the Paleozoic and Mesozoic Era rocks. Prehistoric miners at Spanish Diggings found the prized orthoquartzite in outcrops of the Morrison-Cloverly formations of the Mesozoic Era. Mottled gray quartzites and chert were found in the Morrison formation while colorful and exceptionally fine-grained orthoquartzites were found in the Cloverly formation. The orthoquartzites in the Cloverly came in various shades of gray, yellow, brown, lavender, purple, and red. Not all of the sandstone in the Cloverly formation was silicified enough to produce high-quality orthoquartzites which makes the rock quarries at Spanish Diggings even more exceptional. Outcrops of Morrison-Cloverly cover an area of approximately 1.5 square miles in the vicinity of Spanish Diggings. Those outcrops are bordered by Miocene and Oligocene rocks.  

The Spanish Diggings were some of the largest prehistoric rock quarries in the world. For over thirteen millennia, prehistoric people came to Spanish Diggings and mined orthoquartzite and chert from the hills and valleys. When the prehistoric people left the rock quarries, they carried the raw material with them and spread their finished artifacts and chipping debris across the countryside for hundreds of miles in every direction.

Figure Three – Looking west and slightly south at the hills and valleys of Spanish Diggings.
In the distance is beautiful Laramie Peak. Photograph by Neil A. Waring.

Reher (1991:272) reported a mapping project that calculated the size of Spanish Diggings at approximately 30,000 square meters using the three primary quarry complexes: Barbour, Dorsey, and Spanish Creek. Another 18,000 square meters and approximately 170 stone circles could be included if the campsite and workshop areas near the Barbour quarries were counted. If eleven other clusters of quarries with less debitage were added to the three primary quarries, an additional 120,000 square meters and 500 stone circles could be counted in the Spanish Diggings complex. Reher added that investigators were still discovering additional mining activity and quarry sites at Spanish Diggings. 

Author’s Story Part One: My first memory of Spanish Diggings came from the mid-1960s. I was attending grade school in eastern Wyoming, and if memory serves me, I was in the fourth or fifth grade. The school scheduled an assembly when Jerry and Mae Urbanek were to show us prehistoric artifacts that they found at a place called Spanish Diggings. That was the first time I ever heard of Spanish Diggings, and I was pretty excited about the exhibition. When the school scheduled assemblies I was usually excited for a couple of reasons; assemblies got me out of the dreaded classroom and most assemblies were somewhat entertaining. Secondly, that specific lecture intrigued me because the artifact bug bit me early in life. I had already gone artifact hunting with my family several times and my mother inherited her father’s artifact collection of spearpoints, arrowheads, and scrapers. I was completely fascinated with that collection, and I was hooked on artifacts and prehistory at a very early age.   

My family lived in the right place at the right time for artifact collecting. There was not much to do in rural Wyoming in the 1960s and 1970s except hunt and fish and shoot and explore the outdoors. We were fortunate enough to live in a wide open country with large ranches and mostly friendly ranchers. After I found out about the assembly, I rushed home and told my parents. My mother reminded me that Mae Urbanek was a semi-famous Wyoming historian and author who wrote several books on Wyoming history and its early settlers. That fact only added to my enthusiasm.     

Figure Four - Clovis platter cache found southeast of Spanish Diggings. The material
appears to be Spanish Diggings orthoquartzite. John Bradford Branney Collection.    

Cowboys first discovered the prehistoric rock quarries and mining pits at Spanish Diggings sometime before 1870. At that time, the locals believed that Spanish conquistadors dug the mines in their pursuit of precious metals. A rancher-cowboy by the name of Joseph Stein was often credited with coming up with the name Spanish Diggings sometime around 1882. In 1893, a Cheyenne man named Sidney Bartlett brought more attention to what he called the “Mexican mine” by writing an article about the quarries for the San Francisco Examiner. Stein and another rancher named Lauk were so convinced that there was gold at Spanish Diggings that they hired part-time workers to prospect for gold there from 1886 to 1891. The two ranchers and their workers never reported finding any gold or other precious metals at Spanish Diggings.   

The news about Spanish Diggings eventually caught the attention of academic institutions and museums. In 1894, renowned geologist Wilbur Knight from the University of Wyoming visited the site and documented nineteen mining operations on the north slope of a mesa. He reported vertical shafts, horizontal tunnels, trenches, circular pits, mine debris, and large, crude stone tools. The narrative soon changed from the Spaniards digging for gold to prehistoric Americans digging for toolstone.     

Author’s Story Part Two: The day of the Urbanek show-and-tell did not arrive soon enough for me, but it ended as a huge letdown for this young tyke. At that age, I was not an artifact expert by a long shot, but it seemed to me that Mr. and Mrs. Urbanek showed us a bunch of plain ole rocks that they dubbed prehistoric artifacts. I didn’t know what false advertising was at the time, but that was what I thought of their collection. I expected much more, like my grandfather’s collection with glorious spear points, knives, stone axes, and other cool artifacts. I wonder if I revisited Urbanek’s artifact collection today if I wouldn’t have a different opinion. I imagine their artifacts looked very similar to the artifacts that George Dorsey and associates found in 1891 (figure seven). I learned one thing from the Urbaneks' lecture; I wanted to see Spanish Diggings for myself! That night, I lobbied my parents to take us to Spanish Diggings in the spring. 

Figure Five - George Dorsey
at Spanish Diggings. 

One of the early scholars to visit Spanish Diggings was George A. Dorsey, the curator of the Field Columbian Museum in Chicago. In 1891, ranchers Stein and Lauk picked Dorsey up at the railroad station in Guernsey, Wyoming, and headed out to Spanish Diggings. In 1900, Dorsey published a short paper on his visit to the prehistoric rock quarries. The following paragraph was Dorsey’s observation after studying one of the many outcrops of orthoquartzite in the Cloverly formation.    

“Examining one of the walls of the wash we find a solid stratum, thirty or more feet thick, of flint, or rather of sandstone, which has been worked by silicious waters, thus forming quartzite. This stratum is of variegated color, passing from yellowish brown to violet gray, varied with shades of pink, violet, yellow, purple, etc., the whole stratum thus producing a most beautiful and remarkable color effect.”

-George A. Dorsey (1900:238-239)

Figure Six - Sketch map of Spanish Diggings area by R. F. Gilder (Holmes 1919).      

Dorsey was not alone in visiting Spanish Diggings. There were many organized expeditions by scholars and visitors in the late 1800s and early 1900s. Most of the expeditions were focused on filling barrels and wagons with artifacts and raw materials to take back to their colleges and museums. There was little research done on the rock quarries themselves or the prehistoric people who created them. Some of the early artifact finds reported were digging tools made from antler, stone, and bone; rock wedges; and grooved mauls. For several decades, countless crusades of scholars, recreationists, flintknappers, and artifact collectors carted off thousands of tons of artifacts and raw material from Spanish Diggings, creating a huge archaeological data gap and forever altering the quarries’ prehistoric record. That data gap did not stop George A. Dorsey from prognosticating how the prehistoric miners exploited the raw material at Spanish Diggings.  

“The upper two or three feet of rock is very brittle and does not chip well; indeed, it occurs not as a solid mass, but, owing to long weathering, in long thin sheets or irregular blocks.

“After the soil had been penetrated, the workmen encountered the upper unworkable rock through which it was necessary to excavate to a considerable depth before the denser masses of workable material and the jasper and chalcedony nodules were encountered. On account of the broken character of the upper mass of the quartzite bed such excavations were not necessarily difficult operations. Furthermore, it is possible to believe that this work could be carried on with tools similar to those which would be found efficacious in working the exposed stratum down in the valley.”

-George A. Dorsey (1900:240)

Figure Seven - Typical quarry finds from 
Dorsey's expedition to Spanish Diggings.  

Quartzite was the most abundant tool stone that prehistoric Americans mined at the Spanish Diggings rock quarries. There are two types of quartzite. The first type is metaquartzite which started out as a sedimentary rock called sandstone. In metaquartzite, the original sand grains and silica cement were recrystallized through heat, pressure, and chemical action by a geological process called metamorphism. Metaquartzite is very hard because it is primarily quartz. Metaquartzite tends to have deformed interlocking quartz grains (Andrefsky 2005).

Spanish Diggings is famous for a second type of quartzite called orthoquartzite or silicified sandstone. Orthoquartzite is a clastic sedimentary rock called sandstone which was made almost entirely of quartz sand grains. In orthoquartzite, the quartz sand grains were not deformed like metaquartzite but instead were bound together with silica cement through a geological process called silicification. The prehistoric miners at Spanish Diggings discovered that the high-quality, fine-grained orthoquartzites were near perfect for making tools and projectile points.  

 

Figure Eight - A knife form with a broken tip that I found on one of my earlier visits to Spanish Diggings. The prehistoric individual used orthoquartzite from one of the quarries.    

Author’s Story Part Three: If you ask a Wyoming native when spring will arrive, he or she might inform you that spring arrives in June. If you inquire when summer begins, that same Wyoming native might tell you summers begin sometime in early July and end in August. If you question what the rest of the year is called, that same Wyoming native will inevitably answer, “Winter in Wyoming!” 

Spring finally arrived in Wyoming and my family was ready for their pilgrimage to Spanish Diggings. My parents knew a rancher from our church who owned a big chunk of Spanish Diggings. The rancher gave us permission to hunt rocks on his property and even mentioned that we might find some “petrified turtle shells” if we were lucky. He even drew us a little map of how to get there so that we did not get lost. Even today, Spanish Diggings is not an easy place to find.

My father drove us to Spanish Diggings in our Chevy station wagon. I remember the roads became progressively worse the closer we came to Spanish Diggings on the map until we were traveling on what was best described as a glorified cow trail. My father stopped smack dab in the middle of a wide ravine filled with sagebrush and rattlesnakes. The ground next to the car was littered with chunks of orthoquartzite and chert cobbles from the mine pits. There was so much refuse on the ground that it made hunting for artifacts nearly impossible. It was literally like looking for a needle in a haystack. We spent the day hiking up and down the hills. We found a few primitive tools and worked pieces but nothing special. Our little adventure was probably not worth the wear and tear on our car. The best finds of the day were five or six fossilized turtle shells. I remember finding those as if it was yesterday. I often wonder what happened to those fossils. I regret not taking better care of them.  

Figure Nine - 
SHADOWS on the TRAIL Pentalogy 

I worked on a large ranch and farm a few miles northwest of Spanish Diggings every summer in high school and through a summer or two of college. I occasionally visited Spanish Diggings on my dirt bike in the evenings after work. I found nothing but broken cobbles and crude hammerstones. In all my visits to Spanish Diggings, I only found one small projectile point made from chalcedony. From what I read in the literature, my lackluster result in finding finished artifacts was not much different than that of the early scholars and visitors. When explorer William Henry Holmes visited Spanish Diggings in the early twentieth century, here was how he characterized the trip.

“Nothing whatever was found in the finished state, and even partially worked specimens were not numerous. The refuse about the pits is characterized by the large size of the partially shaped rejects.”

-W. H. Holmes (1919:213) 

Prehistoric Americans came to the quarries, selected good pieces of raw material, roughed them out, and took them elsewhere to finish them up as stone tools and projectile points. Looking back at the grade school assembly, the Urbanek collection might not have been so bad after all. Rough slabs and barely worked cobbles of quartzite and chert were probably typical, even back in the early cowboy days. Perhaps that was the reason why the early cowboys thought Spaniards dug the mines and not prehistoric Americans; the mine debris on the ground was not indicative of who created it!

These days I find a lot of artifacts made from orthoquartzite. I suspect the raw material came from Spanish Diggings but that might not be the right conclusion. Like other popular high plains raw materials like Knife River or Flattop, Spanish Diggings orthoquartzite has its own imposters and lookalikes coming from other areas. I even discovered a prehistoric rock quarry in northeastern Colorado where the orthoquartzite looks remarkably similar to a few flavors of Spanish Diggings orthoquartzite.   

Well, that’s my story. I hope you enjoyed it. No matter what happens to Spanish Diggings or me in the future, I will always cherish those early memories of Spanish Diggings!            

References Cited

Andrefsky, William Jr. 2005. Lithics – Macroscopic Approaches to Analysis. Cambridge University Press. Cambridge.  

Dorsey, George Amos. 1900. An Aboriginal Quartzite Quarry in Eastern Wyoming. Field Columbian Museum, Publication 51, Anthropological Series, Volume II, Number 4. Chicago. 

Holmes, W. H. 1919. Handbook of Aboriginal American Antiquities. Part I – Introduction to Lithic Industries. Smithsonian Institute. Bureau of American Ethnology. Bulletin 60. Washington D.C.   

Reher, Charles A. 1991. Large Scale Lithic Quarries and Regional Transport Systems on the High Plains of Eastern Wyoming – Spanish Diggings Revisited in Raw Material Economies Among Prehistoric Hunter-Gatherers edited by Anta Montet-White and Steven Holen. University of Kansas Publications, 19.   

     

About the Author

John Bradford Branney grew up in Wyoming and from an early age developed a passion for everything prehistoric. He has amassed and documented a huge collection of prehistoric artifacts and fossils. After high school, Branney earned a B.S. degree in geology from the University of Wyoming. Branney then chose a career in the oil and gas industry where he worked for thirty-plus years. During that career, he earned an MBA in finance from the University of Colorado. Branney has written numerous magazine and journal articles about prehistoric artifacts and high plains archaeology. He is currently writing his twelfth book and the sixth book in his prehistoric adventure series the SHADOWS on the TRAIL Hexalogy.    

All That Glitters Is Not Gold (and Not All Brown Cherts Are Knife River)

All That Glitters is Not Gold

(And Not All Brown Cherts Are Knife River)

by John Bradford Branney

 

Figure One - 3.8-inch-long Besant knife form made from Knife River and surface found
on private land near New Town, North Dakota by Sherry Christianson.
Note color, white/yellow splotches, plant fossils, loose hinges, and patina.
John Bradford Branney Collection. 

I am an artifact hunter and prehistorian who spends much of my spare time hunting rocks on the high plains of Wyoming and Colorado. When I think about the most popular raw materials for toolmaking during high plains prehistory, I think of beautiful Hartville Uplift Jasper or Spanish Diggings Quartzite or Flattop Chalcedony, or the subject of this article: Knife River Chalcedony. I would be remiss if I did not mention that there were literally hundreds of different types of raw materials from Alberta, Canada to the Panhandle of Texas for prehistoric people to choose from. Some of those raw materials have local or regional names such as Big Horn Chert or Pryor Creek Jasper or Black Forest Silicified Wood while other raw materials just go by a generic rock type name such as moss agate, tiger chert, or caramel-colored jasper. Maybe someday I will write an article about the less glamorous high plains raw materials. 

Figure Two - BEYOND the CAMPFIRE, the fifth book in the
SHADOWS on the TRAIL Pentology. 

Based on archaeological evidence, it is clear that prehistoric people sought the highest quality raw material that was available to make their tools and projectile points. The ideal raw material fractured conchoidally in a predictable manner and was not too soft or brittle to hold a sharp working edge. Besides availability and quality, a rock type’s flashiness was also a factor for prehistoric people. Knife River Chalcedony checks all the boxes; it was available and of high quality, and it was definitely beautiful. Based on archaeological evidence, prehistoric people went out of their way to scavenge and use Knife River Chalcedony.

You will notice that I called Knife River a chalcedony, but Luedtke (1992:6) would argue with my definition. Luedtke pointed out that chalcedony is the only variety of chert that scientists can identify microscopically by its fibrous form. Those fibers cannot be seen with the naked eye. Luedtke proclaimed that while most cherts made from chalcedony were translucent, not all translucent cherts were chalcedony. She added that Knife River was the perfect example of a translucent chert that was not a chalcedony but a granular quartz, and not a fibrous quartz.

 

Figure Three - Note Knife River translucency on this 2.5-inch-long Middle Archaic Oxbow
Knife Form surface found on private land near Gillette, Wyoming by Chuck Carlson.
John Bradford Branney Collection.   

The most popular name for Knife River Chalcedony by far and used by archaeologists and collectors alike is Knife River Flint which is oftentimes abbreviated as KRF. According to Luedtke (1992:140), the definition of flint is a “homogenous, high quality chert, especially the dark gray or black cherts that form in the Cretaceous chalks of Europe”. That does not fit Knife River any more than the definition of chalcedony does. The most accurate name is probably Knife River Chert because the term chert casts a wide net by including most varieties of microcrystalline quartz.

Since an old habit is hard to break, I will refer to the rock type as either Knife River Chalcedony or just plain Knife River for this article. Secondly, I will refer to Knife River Chalcedony as semi-translucent even though some authors prefer to call it translucent. When I think of something translucent, I think of a clear pane of glass, and Knife River is not as translucent as a clear pane of glass.   

Luedtke (1992:6) described Knife River as a very dark brown, fine-textured, silicified lignite with a medium luster and a depth of translucency from 5 to 11 mm. Bates and Jackson (1984:295) defined lignite as a brownish-black coal that was intermediate in coalification between peat and sub-bituminous coal. The adjective silicified describes a process where organic matter, in this case lignite, became saturated and replaced by silica in the form of quartz, chalcedony, or opal.  

Figure Four - 2.8-inch-long Goshen spear/knife form surface found on private land in the 
Sand Hills of Lincoln County, Nebraska. John Bradford Branney Collection.  

Kristensen et al. (2018:22) analyzed Knife River using macroscopic, microscopic, and geochemical techniques and supported the description that the rock type was silicified lignite. The authors described the color of Knife River as blonde to dark coffee brown and stated that the rock type could possess high translucency, visible bedding planes, plant microfossils, and white splotches. The authors also declared that by just using visual inspection, Knife River could not be discerned from silicified peat or chalcedony.

Geologists know very little about the origin of Knife River Chalcedony because it is only found in secondary deposits and not in its original geological context. Hickey (1966:64-5) suggested that based on its high carbon content, plant fossils, and proximity to unsilicified lignite, Knife River originally formed as a deposit of organic lignite in the Eocene geological period. He surmised that later in the Oligocene geological period, silica-rich groundwater saturated the lignite, creating a hard silicified lignite layer. Kristensen et al. (2018:3) reported that by the time Paleoindians showed up to exploit the rock type in the late Pleistocene geological period, the silicified lignite bed was eroded away and broken up into pebbles, boulders and cobbles of Knife River.  

Figure Five - Knife River nodules found in secondary geological contexts from eroded bedrock outcrops that no longer exist. The images on the left and top right are courtesy
of David McDonald. The bottom image on the right is courtesy 
of the Archaeology and Historic Preservation Division, 
State Historical Society of North Dakota.

Clayton et al. (1970) expanded on that interpretation by postulating that the original Knife River lignite bed was initially surrounded by the clays, silts, and sands of the Golden Valley Formation of Eocene age and underlain by the clays, silts, sands, and lignite beds of the Sentinel Butte Formation. Earlier, Benson (1949, 1952) informally divided the Golden Valley Formation into two members, a brightly colored claystone called the Bear Den Member of Paleocene age, and an overlying unit called the Camels Butte Member of Eocene age. Both members were deposited roughly between 50 and 57 million years ago.

Knife River’s color is often compared to “root beer, coffee, or beer bottle” with a touch of translucency. Many prehistoric artifacts made from Knife River are beautiful and glow in vivid shades of brown when backlit (figure three). I have seen collectors pay a pretty penny for prehistoric artifacts made from a desirable chunk of Knife River raw material. Market demand combined with a plethora of lookalike materials from Texas to Alberta led to the overidentification of Knife River as the raw material. Collectors and archaeologists must be careful when they use visual inspection alone to identify Knife River from other semi-translucent brown cherts or chalcedonies.

Figure Six - Agate Basin spear/knife forms made from semi-translucent to opaque Knife River 
and surface found on private land from North Dakota to northern Colorado. These
examples show color variation, white splotches, hanging hinges, and patina.  
The longest Agate Basin is 4.7-inches-long.
John Bradford Branney Collection.  

I have quite a few prehistoric artifacts in my collection made from Knife River Chalcedony, found from the Dakotas and Montana through Wyoming and south to northern Colorado. The artifacts range in color from very dark brown to honey-colored brown. Most of my Knife River artifacts exhibit a certain degree of translucency, but I have a couple of nice examples that are completely opaque. When I visually inspect an artifact, I use five characteristics to identify Knife River. The first characteristic is its color as described in a few sentences above. The second characteristic is the silicified plant fossils or palm fronds captured in the matrix of the rock. The third characteristic is a distinctive white-to-yellow patina caused by chemical weathering and commonly found on Knife River artifacts. The fourth characteristic is the distinctive white and yellow opaque splotches on the surface of the rock or locked into the matrix. The fifth characteristic that cannot be used as a diagnostic feature for Knife River but is quite common on Knife River artifacts is loose hinge fractures, even when the artifact was found in freeze-thaw country.  I have examples of Knife River artifacts with all five characteristics and I have suspected Knife River artifacts with none of those characteristics. If a person does not notice at least one of those characteristics, they might be looking at a Knife River lookalike.     

A few artifact collectors and authenticators believe that UV irradiation can be effectively used to identify Knife River as the rock type and for authenticating Knife River artifacts. That theory contends that authentic Knife River artifacts fluoresce under either short or long-wave UV light. The assumption is that authentic artifacts are aged and chemically weathered therefore they fluoresce, while the fresh surfaces on artifact reproductions won’t fluoresce. One authenticator even told me that authentic Knife River artifacts emit an orangish color under UV light when they are authentic. To test that theory, I did my own experimentation with a few of my Knife River artifacts. I did not obtain the same results as the authenticator. Of the artifacts that did fluoresce, some appeared slightly orange while others appeared almost white or some shade in between. A few artifacts fluoresced so weakly that I needed my imagination to see any fluorescence, and a few artifacts did not fluoresce at all. To ensure that the Knife River artifacts did not need to be a certain age to fluoresce, I experimented with artifacts ranging from Paleoindian to Late Prehistoric times. I concluded that using UV irradiation as a method for determining rock type or authentication of Knife River artifacts was indefinite at best.

Figure Seven - Lookalike material or Knife River Chalcedony? Several professionals and 
collectors have looked at this 1.8-inch long Folsom dart point, both macroscopically and 
microscopically and we have a hung jury on whether it is Knife River or not. 
John Bradford Branney Collection.  

Kirchmeir (2011:27) and Kristensen et al. (2018:14) experimented and determined similar results with UV radiation and Knife River. The investigators noted that artifacts made from similar materials, such as brown chalcedony and silicified peat, fluoresced in a similar manner as Knife River. In their studies, Knife River and lookalike materials showed such a wide range of fluorescence to non-fluorescence that the process was not useful for the identification of the raw material. The investigators warned that chemical weathering of the rock could enhance or obscure its fluorescence. Their conclusion was that UV irradiation was not an effective standalone technique for the identification of Knife River and should only be used in concert with other macroscopic, microscopic, and geochemical analyses.

What separated Knife River from most high plains raw materials were its overall abundance and wide distribution. The archaeological evidence that Knife River traveled far from its source during prehistoric times is overwhelming. The rock type originated from a network of rock quarries in North Dakota that supplied a vast amount of tool stone for prehistoric humans for thousands of years. Knife River’s popularity is reflected in the number of prehistoric tools made from it, the quarries’ endurance over prehistoric times, and the rock type’s dispersal across the plains.

Ahler (1986:105) estimated that prehistoric people quarried around 12.5 million kilograms (20,393 tons) of Knife River Chalcedony from roughly thirty quarry sites in a primary source area of approximately 2,000 square kilometers (772 square miles) in Dunn and Mercer Counties in North Dakota. From his estimates, Ahler calculated that prehistoric people made around 640 million tools and cores from Knife River and spread those tools and cores over an area of approximately 3.7 million square kilometers (1.4 million square miles). Whether Ahler’s estimations were accurate or not we will never know for sure, but even if we divide Ahler’s estimates by a factor of twenty, the numbers remain staggering. Knife River Chalcedony was quite popular with the prehistoric folks!

 

Figure Eight - Lookalike material or Knife River? This root-beer colored Scottsbluff point was 
surface found on private land near Green River, Wyoming. Artifact authenticator Greg Perino
identified the material as Knife River, but it could be one of the local brown chalcedonies
found in that region. The point is 2.5-inches-long. John Bradford Branney Collection.       

Steuber (2018) addressed the wide distribution of Knife River by determining whether or not archaeologists and collectors were overidentifying Knife River on the high plains. She challenged the entrenched professional view that Knife River was the dominant material in Besant/Sonota prehistoric cultural sites on the Northern Plains. Steuber chemically analyzed twelve brown chalcedony sources across three Canadian Provinces and three American States. She then compared her chemical analysis with material labeled as Knife River at archaeological sites. She concluded that Knife River was not the dominant lithic raw material at those archaeological sites after all and that the prehistoric inhabitants were exploiting local varieties of brown chalcedonies and not as much Knife River as previously reported. Steuber concluded her analysis by quoting, “All artifacts made from brown chalcedony should be referred to as such and not as KRF unless they have been previously geochemically characterized”.  

I have discovered several prehistoric rock quarries and mining operations in my search for prehistoric artifacts on the high plains and I can conclude that while the raw materials at those quarries met the knapping and durability requirements for toolmaking, the distribution never came close to the Knife River supply chain. Knife River Chalcedony was one of the kings of high plains raw material for thousands of years.      

References Cited

Ahler, S.A. 1986. Knife River Flint Quarries: Excavations at Site 32DU508. State Historical Society of North Dakota, Bismarck, North Dakota.

Bates, Robert L. and Julia A. Jackson. 1984. Dictionary of Geological Terms. Third Edition. Anchor Press/Doubleday. New York.

Benson, W.E. and Laird, W.M., 1947, Eocene of North Dakota: abstract, Geological Society of America Bulletin, v 58, p. 1166-1167.

Benson, W.E., 1952, Geology of the Knife River area, North Dakota: U.S. Geological Survey Open-File Report, 276 p.

Clayton, L., W.B. Bickley, Jr., and W.J. Stone. 1970. Knife River Flint. Plains Anthropologist 15:282-290.

Hickey, L.J. 1966. The Paleobotany and Stratigraphy of the Golden Valley Formation in Western North Dakota. Ph.D. dissertation, Department of Geology, Princeton University, Princeton, New Jersey.

Kirchmeir, P.F.R. 2011. A Knife River Flint Identification Model and its Application to Three Alberta Ecozone Archaeological Assemblages. M.A. thesis, Department of Anthropology, University of Alberta, Edmonton, Alberta

Kristensen, Todd, Emily Moffat, M. John, M. Duke, Andrew J. Locock, Cody Sharphead, and John W. Ives. 2018. Identifying Knife River Flint in Alberta: A silicified lignite toolstone from North Dakota. Occasional Paper No. 38. Archaeological Survey of Alberta.  

Luedtke, Barbara E. 1992. An Archaeologist’s Guide to Chert and Flint. Archaeological Research Tools 7. Institute of Archaeology. University of California, Los Angeles. 

Steuber, Karin Ingrid. 2018. Geochemical Characterization of Brown Chalcedony during the Besant/Sonota Period. Ph.D. Dissertation. Department of Archaeology & Anthropology, University of Saskatchewan, Saskatoon.

About the Author

John Bradford Branney has hunted and collected artifacts for six decades and he has written about his adventures for around three decades. Join Author Branney for his high plains saga about the lives of Paleoindians some twelve thousand years ago in the SHADOWS on the TRAIL Pentalogy. His books are available on Amazon.com or wherever fine books are sold.     

Alibates Agatized Dolomite - Rock Types Along the Trail

 by John Bradford Branney

 

Figure One - Artifacts from the author's collection, made from various flavors of Alibates  
agatized dolomite. Tear-drop ultrathin knife form to the right is 3.25 inches long.    

My story begins thirty-five or so miles northeast of Amarillo, Texas on what is now known as the Alibates Flint Quarries National Monument. The monument encompasses 1371 acres with over 700 visible prehistoric mining pits. For 13,000 years or more, prehistoric humans mined a special rock type that they used to make their projectile points and stone tools from the quarries. In the following paragraphs, I will delve into some of the history, prehistory, and geology surrounding a special rock type known as Alibates agatized dolomite. 

 Alibates National Monument around Lake Meredith. 
Graphic by Jason Kenworthy
(NPS Geologic Resources Division). 

Alibates agatized dolomite is a very distinctive, multicolored rock with colors ranging from maroon to red and gray to black. Mix in a little white and tan with bands of pink, blue, purple, yellow, purple, brown, and cream, and Alibates agatized dolomite exhibits a rainbow of colors (figure one).

Although Alibates agatized dolomite is the rock type’s “official” name, collectors and professionals alike refer to it by other names such as Alibates, Alibates chert, Alibates jasper, Alibates dolomite, Amarillo flint, Beef Steak Alibates, Quartermaster flint, and Alibates silicified dolomite. In this article, I will refer to the rock type as either Alibates agatized dolomite or just plain Alibates.

According to several modern-day flintknappers I spoke to, Alibates can have a resistant quality and hardness that makes it difficult to sometimes knap. As popular as Alibates was during prehistoric times, based on its wide geographical range, prehistoric flintknappers must have ignored the rock’s finicky nature and instead focused on its exotic colors and banding. I believe that Alibates probably mesmerized prehistoric humans just like it does some of us today. Alibates agatized dolomite is not only pleasing to the eye, but perhaps prehistoric humans believed the rock enhanced their hunting success. 

     Figure Two - Boulders of white Alibates Dolomite cascading

down hills at Alibates Flint Quarries NM. NPS Photograph. 

                                                                                                                 

How did the name Alibates agatized dolomite come about? Gould (1907) first described the agatized dolomite a mile and a half south of the national monument along Alibates Creek in Potter County, Texas. A local rancher named the creek after his cowboy son, Allen “Allie” Bates, and Gould named the rock type after the creek where he found it. Agatized is an adjective describing the geological process that creates the rock type called agate, which is a striped or banded, sometimes translucent, cryptocrystalline variety of quartz. And the last word in the rock type’s description, dolomite, is a common, rock-forming mineral that I will discuss later in the article. 

Meltzer (2006:250) added some flavor to the origin of the name Alibates agatized dolomite by relaying the following story. In 1926, excavations began at the original Folsom site in New Mexico. In 1928, the American Museum of Natural History joined the Folsom excavation with vertebrate paleontologist Barnum Brown in charge. In November of 1930, Oklahoma State Geologist Charles Gould sent Barnum Brown a package of Alibates agatized dolomite. Gould acquired his experience in Texas Panhandle geology several decades prior to 1930. Gould also happened to be the first person to map and describe the Alibates Dolomite Formation where the agatized dolomite came from. 

Figure Three - The Drake Clovis Cache. One of the 
most famous examples of mostly Alibates artifacts
found on the high plains of northern Colorado. 

Barnum Brown did not agree that the rock samples Gould sent him were agatized dolomite. Brown believed the rock samples were jasper, a variety of chert containing iron-oxide impurities which gave the rock type a wide range of colors, especially red. Being an experienced geologist, Gould knew exactly where the rock samples came from. He replied to Brown that the rock samples “formed a constituent part of a ledge of dolomite that outcropped over parts of the Panhandle of Texas”. Gould added that the best site for finding Alibates agatized dolomite was “on the bluffs overlooking the south Canadian River”.

Barnum Brown and Charles Gould probably agreed to disagree on the rock type, but Brown and his associates confirmed that Paleoindians used Alibates agatized dolomite to make projectile points and stone tools at the Folsom site in New Mexico. Long and short of it, the label Alibates agatized dolomite prevails even today.  

The dolomite “on the bluffs overlooking the south Canadian River” that Charles Gould referred to was a fifteen-foot-thick bed of agatized or silicified dolomite and mudstone that geologists call the Alibates Dolomite Formation or the Alibates Dolomite for short. That formation contains three informal members: a lower gray dolomite which is resistant enough to form ledges, an upper brecciated and fractured upper gray dolomite that supplied most of the agatized dolomite, and a red to brown calcareous mudstone sandwiched in between the two dolomites. The Alibates Dolomite Formation lies above the red beds of the Permian Whitehorse Formation and lies below the red beds of the Permian Quartermaster Formation. Geologists often refer to that entire sequence of rocks as the Permian Red Beds. The twelve-million-year-old Ogallala formation from the Miocene-Pliocene Epochs lies directly on top of the two-hundred-sixty-million-year-old Permian Red Beds in what geologists call the Great Unconformity, a massive gap in the geologic record.    

It is now time for us to board our time machine for a little geology lesson. I am setting the dial of our machine for around two hundred fifty-five million years ago during the Permian Period. At that time, North America, and most of the rest of the world were not geographically located where they are today. Texas was situated along the equator and was a small part of a supercontinent named Pangea. During that time period, Texas landscapes were a combination of coastal plains, marine basins, and tidal flats. The Permian Red Beds for the most part were terrestrial deposits and formed alongside a great ocean that extended up from the south.

Figure Four - Pangea in Late Permian. Texas and the Alibates National Monument are
 located near the Equator at the southwestern end of the Central Pangean Mountains.     

Throughout geologic time, climate change has been a big factor in determining both weather and landscape, and the Late Permian in Texas was no different. When colder global climates occurred, thick ice caps grew in the north and south parts of Pangea. To grow, the ice caps borrowed water from the oceans which resulted in lower sea levels and more landmass. During that time in Texas, river and stream systems deposited hundreds of feet of relatively soft shale, sandstone, and mudstone, including where the Alibates National Monument lies today.   

When the climate reversed and warmed up, the ice caps melted, and the water returned to the seas. Sea levels rose and inundated the land with seawater, stretching from the Arctic Ocean near Alaska on the north, through Canada and the United States, and connecting with the Pacific Ocean in Mexico. When sea levels dropped again, lower-lying basins trapped the seawater, and when that water evaporated, it left behind organic matter and salt. That was how thin beds of gypsum formed in the national monument area and the main reason why the Canadian River tastes salty even today. And how was the Alibates Dolomite Formation created?      

Dolomite is a common rock-forming mineral and in its pure state, it is white to light-colored. Chemists specify dolomite as CaMg(CO₃)₂. Jackson (1970:176-178) and Scholle et al. (1983:194-195) studied the modern-day creation of dolomite deposits and reported that the formation of dolomite occurs along the ocean in hot, dry climates, a few inches above high tide in a zone referred to as the supratidal, or the splash or spray zone. The scientists proposed that dolomite started out as calcium carbonate (CaCO₃) in the form of calcite and aragonite sediments, mostly consisting of the remains of plankton, coral, algae, and shelled animals. Seawater soaked the supratidal zone during storm surges and abnormally high tides. Seawater also saturated the supratidal zone from underneath as capillary action pulled seawater to the surface of the zone (figure five). When the seawater evaporated, it left behind magnesium-rich brines which chemically reacted with calcium carbonate to form dolomite. 

Figure Five - Schematic diagram showing sedimentary environments from continental 
to marine, their relationships to sea level, and the relative amounts
of capillary action (Scholl et al. 1983:172). 

For agatization or silicification to occur, silicon dioxide must replace the original dolomite. Bowers and Reaser (1996) reported that at the Alibates National Monument, a silica-based mineral called chert completely replaced the dolomite in the upper dolomite member while only partially replacing the dolomite in the lower member. That led the investigators to conclude that the agatization or silicification process occurred from the top down with the upper dolomite member acting as the main host rock for silica solutions. Bowers (1975) stated that minor amounts of aluminum, iron, and manganese were deposited with the silica in the dolomite and those minerals account for the beautiful bands and colors found in Alibates agatized dolomite.              

Where did the silica come from that agatized or silicified the dolomite? Since the overlying rocks above the Permian Red Beds were eroded away, scientists can only speculate as to the source of the silica. The U.S. National Park Service (2022) provided three theories for the origins of the silica in the dolomite. The first theory entails an eruption of a Yellowstone super-volcano around 675,000 years ago provided silica via volcanic ash. Around Lake Meredith, there are several locations where there is a three-foot thick bed of Yellowstone ash. The theory goes that when it rained, some of the silica-rich ash dissolved into the rainwater and percolated down through the dolomite. Another theory is that the deposition of the Ogallala Formation sediments brought silica-rich material with it. The third theory, the National Park Service proposed was that silicification occurred at the same time as the dolomite formed, but for that to occur, perfect conditions were in order.  

We may never know for sure but what we do know for sure is that Alibates agatized dolomite is a beautiful and desirable rock type for artifacts!         

Bowers, R. L., 1975. Petrography and petrogenesis of the Alibates dolomite and chert (Permian), northern Panhandle of Texas [M.S. thesis]. The University of Texas at Arlington, Arlington, Texas, 155 pp.

Bowers, R. L., and Donald F. Reaser, 1996. “Replacement Chert in the Alibates Dolomite (Permian) of the Texas Panhandle”. The Texas Journal of Science.    

Gould, C. N., 1907, “Geology and water resources of the western portion of the Panhandle of Texas”. U.S. Geological Survey Water Supply Paper 191, pp. 1-70.

Jackson, Kern C., 1970, Textbook of Lithology, pp. 176-178. McGraw-Hill Book Company. New York.

Meltzer, David J., 2006, Folsom: New Archaeological Investigations of a Classic Paleoindian Bison Kill. University of California Press. Berkeley.  

Scholl, Peter A. Don G. Bebout, and Clyde H. Moore, Carbonate Depositional Environments, AAPG Memoir 33, pp. 194-195. The American Association of Petroleum Geologists. Tulsa.

U.S. National Park Service, 2022, Geology-Alibates Flint Quarries National Monument (nps.gov).

The historical fiction novels written by John Bradford Branney are known for their impeccable research and biting realism. In his latest blockbuster novel Beyond the Campfire, Branney catapults his readers back into Prehistoric America where they reunite with some familiar faces from Branney’s best-selling prehistoric adventure series the Shadows on the Trail Pentalogy.

John Bradford Branney holds a geology degree from the University of Wyoming and an MBA from the University of Colorado. John lives in the Colorado mountains with his wife, Theresa. Beyond the Campfire is the eleventh published book by Branney.