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.