Local Rock Hound Discusses Geology of the Widely Known Spanish Diggings

Last updated: April 6, 2020

The Lusk Herald
March 5, 1953

By Elmer C. Postel

(Several years ago Joe McConaughey, Archie Sparks, and Elmer C. Postel set up a camp along the northern boundary of the Spanish Diggings area with the purpose of trying to find a reasonable solution to the many unanswered questions concerning that are. Mr. Postel now makes a report on what the three saw and what they believe must be somewhat neat the truth. Mr. Postel says, “I do not intend this report to be a learned discussion in geology. Neither Joe, Archie nor myself has desk space nor the proper length of beard to enter into any such discussion. It is only meant to help other amateur rock-hounds who may visit the area in the future.”

To get back to the geology of Wyoming let’s take the locality known as “The Spanish Diggings”.

To get a clear picture, let’s go back in “time” to the close of what is called the Jurassic Era which preceded the beginning of the Cretaceous Era. After the sundance sea bed had risen and the remaining ponds and lakes silted up the “Spanish Diggings” area became a non-marine or land horizon or surface. The last of Cordilleran Mountains were worn down and the debris helped to fill in the low spots. As ages pass the accumulations of sands and sediments from all sources built up a layer of surface crust over the whole of lower lands of Wyoming including the Spanish Diggings area. Some of this was lime, some was mud, and among other kinds of sediments, some of it was sands.

As the new era called the Cretaceous came in, the surface of Wyoming began to sink lower and lower and this sinking surface finally became the “Montana sea floor,’ better known as the Cretaceous sea floor. Great pressures were put upon these sediments, and as the ages passed, more and more pressures were added. New sediments piled on top of the original ones that had one been dry land, or to be more exact, non-marine. Some of the more greatly depressed areas became the awful deeps. At least they became the deepest parts of this new Cretaceous Sea. Within them, dust and ashes from volcanoes settled and sank and within them too lie the remains of the kinds of life adaptive to such depths.

From these “deeps” shoreward and into areas of somewhat lesser depths were laid down the sediments known as the Benton Series. They consist of what is called the Granerous, Greenhorn and Carlile in that order shoreward. The original sediments that made up the depressed sea-floor were the Dakota Fuson and Lakota in that order downward. Further in from those of the Benton series already named those of the Niobrara and Pierre. The shallows just off the shore, the river deltas, the bays and so on were what is called Foxhill, while the shore or land itself is known as the Laramie or Lance. All of these main sediments were spread in varying thicknesses over the Dakota surface.

SURFACE RISES
At the close of the Cretaceous Era which lasted about 60 million years, Wyoming’s surface rose once more. The sea drained away and as the lands rose, a new cycle of mountain making began and the Rockies were thrown upward in great fault-blocks.

Under such crustal pressure and from the resulting heat from the magma below a profound change took place in the basic sediments, especially on the Lakota. These basic sediments were changed in character. The Lakota sands were metamorphosed and became crystalline in character and are known as quartzite. The sands and muds above were changed into a formation that appears to have been burned or fused---such is the “Fuson”. Above, this is the old original top soil containing plants, leaves, and the remains of a non-marine deposit. It is called the “Dakota”.
Now, then, when this old non-marine surface was brought back upward into folds and ridges of the flanks of the higher mountains, erosion soon swept them free of the sea deposits as low ridges of hills. Erosion continued.

EROSION REVEALS QUARTZITE
Such is the character of the Spanish Diggings area. These older deposits being much the harder, remain. Some of these ridges and hills have eroded away to where only the rocks of the Lakota quartzite remain on the surface today. These eroded ridges or hills account in large measure for much of the quartzite supposedly carried out by the minders or diggers. Some of the material was, of course, carried out to wherever the Indians had established their camps, to be worked on by the ladies perhaps in their spare time, or by the men when they were free of the “hunting necessity” for the camps’ food.

Much of this Lakota quartzite is either exposed or is near enough to the surface to be obtained by no great amount digging. Quartzite of many beautiful colors could now and then be obtained by the simple removal of that not so pretty. This, along with the fact that here and there “fold fractures” were found which made the job of getting at the deeper and prettiest colored rocks easier, accounts for the “pits” or “mines.

USED FOR TOOLS
For unknown generations the ancestors of the Indians found here used this rock for tools all kinds. Perhaps those to first find and make use of this quartzite had no horses yet and had to carry this equipment or perhaps use dogs to haul his belongings. Probably until the horse was acquired these Indians roamed about much less than they did later. Their camps were of much longer duration. Some sort of simple farming probably was practiced and since no great distance was involved when a camp was moved, larger tools could be kept. These tools need not, therefore, to be so exact nor so well made since a new supply was close by. Many of the tools were large, awkward, and crudely chipped. Nevertheless, as the years rolled by into centuries some of these tools, or “artifacts” as they are called, became scattered far and wide, some even reached to points east of the Mississippi River, passed no doubt from tribes in trade. It is well known the Indian loved bright colors in everything, even in his tools. So, no wonder quite a lot of effort was made in his search for beautifully colored rocks. Hence the “pits” and so much discarded dull colored material. Probably the bow and arrow was to replace the spear and club long ages after many of the pits had been exploited. After more and more of the escaped horses once owned by the invading Spaniards to the southwest were acquired by the Indians, a need arose for smaller and better made tools. Enough of these tools had to be carried to last on longer and longer hunting trips. So more and more pains were taken to made better and smaller tools. As time went on this art was acquired t almost perfection by some of the tribe members as is attested to by the beautiful artifacts found locally, made from the quartzite of the Spanish diggings area.

No amount of legend for tall-tales by “tongue-artists” can produce a lost tribe of miners for the area. Nor is there any record that any Spanish people ever saw the area.

The simple accumulation of work done for centuries by the early Indians who from generations to generation passed on the work as well as the work-sited itself to their descendants fully accounts for the Spanish Diggings and all that we see there now.

DINOSAUR BONES FOUND
At lower levels within the area can be found the still older Jurassic sediments underlying the Lakota quartzite of the Cretaceous Era. At some of these older levels can be found dinosaur bones that were washed into the ancient Sundance-sea along with the fossil remains of the belemnites (B. Densus) whose cigar shaped “pens” can be found in quantity by anyone who cares to look for them.

Along the more northern boundary of the area are strata from Sundance to the Dakota “Hogback” ridge tops. Some of these strata are now seen to be almost vertical. Much crushing of sediments took place during the disturbance which probably had its beginning beyond the Jurassic and during the Lower Carboniferous or Mississippian of the Paleozoic Epoch. This disturbance called the Hartville uplift extended from the Black Hills of South Dakota to the Colorado Mountains. It was a disturbance that from era to era took place and acted as a sort of hinge-line causing a weak fracture in the earth’s crust along its whole length. The Spanish Diggings are on this hinge-line as is the “Cow Gulch” area where all of the already mentioned stratas as well as the same types of fossils may be seen. Along with all this, may also be found a few pits reaching down into this same Lakota Quartzite.

GRANITE EXPLAINED
When the magmas surged upward forcing these strata upward into fold and ridges the core materials almost reached the surface. These may be seen as the now exposed granite outcrops south of Lusk. This magma has since been used as monument material and has been cut and polished in Lusk and in the town of Jay Em.

From these granite outcrops, westward can be traced the strata steps upward through the Paleozoic Epoch into those of the Mesozoic where after reaching Douglas, the Green Horn becomes the hills just south of that town. Swinging around to the northwest and north, the strata passes into the Pierre, the Fox Hill and on into the Lance shore line of the old Cretaceous Sea. Over some area of this Lance horizon is spread the Fort Union strata of the Paleocene, or basic Tertiary. In this latter may be found the fossil remains of the archaic mammals of the period. Within these folds of strata and on the west and north side of some of them were trapped the oil pools of “Big Muddy,” Glenrock, Lance Creek, and others.

The “Cow Gulch” area is a pivot point of the disturbance. Here the tilt or strike is from the southeast and east towards the west. Therefore, from “Cow Gulch” eastward strata steps leading upward into the Pierre have been traced by myself to the east of the Boner ranch. I do not know if there remains any evidence of newer stratas above the Pierre such as the Foxhill and Lance to the eastward or not. These many have been eroded away before the Tertiary deposits which seem to overlie the Pierre in that eastward direction, were laid down.

It seems quite likely that other pivot points occur to the north of Cow Gulch with a reversal of the “strike” first to one side, then to the other of the fault hinge-line, ending at last with the Black Hills of South Dakota.

ANCIENT CULTURE EXISTED
It is evident that the last disturbance occurred just at the close of the Mesozoic and before the Tertiary deposits which do not show any such disturbance was laid down over the area. However, since much of the Fort Union of the Paleocene is gone and an overlying Eocene strata is to be found locally, perhaps this disturbance did not wholly end until well into the Eocene period of the Tertiary. Since there is no remaining Eocene deposit and the Fort Union or Paleocene deposits are so far removed from the actual fault-line, there remains no actual “strike” to prove that it was a part of those strata faulted. Oligocene strata show no faulting. It is evident, also, that a far more advanced ancient culture once existed in Wyoming than that of the ancient Plains Indians. Yet, no evidence of such a people is to be found at the Spanish Diggings. The evidence is to the contrary there seems to point to a beginning of the crudest kind.

So far I have found no Yuma evidence nearer than “Old Woman Creek” north of Lusk. The artifacts of Yuma origin may have been transported to that location either by the later Plains Indians or by flood waters of Old Woman Creek, since those found were in the creek bed itself. Many artifacts of the Plains Indian origin were also found in the same locality.

All of this is in no way written to lessen the value of the Spanish Diggings area. It is one of the very few and best spots in all of Wyoming where the continuous record of the Plains Indians may be studied. For that reason the area should be made a memorial park to the Plains Indian and protected as such against vandalism—yet open to study by the students of the future.

From the geologic standpoint, the Spanish diggings area is but a small part of a much larger picture, one that has as its basic cause, the earth’s crustal contraction resulting from an effort throughout the ages to conform to an ever shrinking core.







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