Wednesday, July 30, 2014


Living and teaching in western Kansas did not allow much interaction with either igneous or metamorphic rocks, nor with Paleozoic rocks older than the Mississippian (and these age rocks are restricted to the southeastern most 50 sq. miles of the state).  So, what to do?  How could a geology student become better acquainted with rocks that are not Tertiary, Cretaceous, Permian or Pennsylvanian in age?  Well, it seemed like an easy answer—road trip!  So off we went either south or west, depending upon the time of year.  In early fall the Colorado mountains were beautiful with color and outcrops vacant of people. During the spring semester Colorado was often cool-cold and snow lingered in the high country.  Therefore, Oklahoma to the south seemed like a good choice.  And, the most interesting places to visit were the Wichita Mountains in the southwest, and the Arbuckle Mountains in the south central part of the state.

 Geologic map of Oklahoma (from Oklahoma Geological Survey).  The Arbuckle Mountains are located to the south of Oklahoma City (and a little east) while the Wichita Mountains are to the southwest. Both appear on the map as isolated “blobs.”

These two ranges present some very interesting stratigraphy and geologists still seem to be debating about the origin of the “basement rocks” cropping out in the mountains.  If readers would travel to Colorado or Wyoming or New Mexico (and other western states) they would note that the oldest rocks, especially in the Laramide front ranges, are Precambrian in age—older than ~542 Ma.  However, the igneous rocks, lots of rhyolite, granite and diorite, in the Wichita Mountains are perhaps latest Precambrian (Neoproterozoic: 1000Ma to 542 Ma) but are mostly Cambrian in age, something younger than ~542 Ma. And, that is the really interesting part .

Location of the Southern Oklahoma Rift System penetrating the continent at about 90 degrees to the edge of the continent.  Map taken from Hansen and others, 2011.  

The Wichita Mountains are situated in the southwestern part of Oklahoma  and actually have some relief, maybe 500 to 1100 feet, and dominate the topography.  I remember climbing Mt. Scott  at ~2462 feet and essentially the highest peak in the range; Mt. Pinchot at 2479 feet is on a special area of the wildlife refuge and off limits to visitors, while Haley Peak on private property is 2481 (maybe). The oldest rocks in the Wichitas are known as the Tillman “metasedimentry group” and represent latest Precambrian-early Cambrian marine sandstones that are now turned to quartzite.  However, beginning at about the same time as their deposition, massive volcanism and plutonic placement of granite was beginning in a structural basin termed the Southern Oklahoma Rift System (SORS).  Some geologists argue that the SORS sequence represents a sea floor spreading event, a rift-rift-rift triple junction, with one arm extending into the old proto-North American continent (known to geologists as Laurentia) while the other two arms are now obscured by ocean basins (Hansen and others, 2011).  The Oklahoma arm has been  given the name Southern Oklahoma Aulacogen or Wichita Aulacogen since the arm ultimately failed (an aulacogen). However, Thomas (2011) believed the plutonic events are part of a large fault zone extending inward into the proto continent.  These magmatic rocks in Oklahoma also seem related to other igneous events stretching from New Mexico to Utah and Colorado.  Whatever the cause, the igneous rocks in southwestern Oklahoma (latest Precambrian? to Cambrian in age) represent a major tectonic event along the southern margin of proto North America; the older Raggedy Mountain gabbro group and the Navajoe Mountain basalt group are unconformably overlain by the widespread Carleton Rhyolite Group and the intrusive Wichita Mountain Granite Group.  The latter two units are the igneous rocks that form the rugged mountains and are well exposed and easy to observe.  All in all, the Wichitas are a great place to visit, to observe the buffalo (bison) at the wildlife preserve, and see some igneous “basement” rocks that are not Precambrian in age.

 Mt Scott in the Wichita Mountains is the most easily accessible peak in the Range. Public Domain photo.

Map showing location of the Wichita Mountains in southwestern Oklahoma.  Igneous rocks dominate the mountains in the south, near Fort Sill, and are the most visited section.  North of the Meers Fault there are large exposures of the Ordovician (488-443 Ma) Arbuckle Group limestones.  Map taken from Hansen and others, 2011.
Mt. Sheridan with granite (light-colored) overlying dark-colored gabbro.  Public Domain photo.
Starting before the conclusion of the Wichita magmatic event, and continuing after, sediments begin to erode from the surrounding highlands into the rift or fault basin (SORS).  In addition, marine sedimentary rocks, limestone, sandstone, shale, were deposited, on and off, in Oklahoma from late Cambrian through the early Mississippian (~359-345 Ma).  By the late Mississippian (~328-318 Ma), SORS was rapidly subsiding and filling with clastic particles later forming a shale.

By the Pennsylvanian (beginning ~311 Ma ) “things” begin to change in Oklahoma as a result of what is termed the Ouachita Orogeny—plates of South America and Africa bumping in to the southern margin of North America.  In Arkansas and parts of eastern Oklahoma (see previous Blog) the collision resulted in formation of thrusted and folded mountains called the Ouachita Mountains.  In the Mountain West states, the collisional event produced large block fault mountains—the Ancestral Rocky Mountains.  And in southern Oklahoma, the old SORS was no longer accepting sediments but was activated by vertical uplift and faulting into a highland area and shedding off large clasts that later cemented into sandstones and conglomerates.  The erosion continued into the early part of the Permian (~251 Ma) but by but the late Permian (~290 Ma) the mountains (uplifted SORS) were covered and buried by sediments.  Jurassic and Triassic (~228-145 Ma) rocks are virtually unknown from western Oklahoma and Cretaceous (~145-65 Ma) rocks were probably deposited but are mostly eroded away.  The current Wichita Mountains are the result of landforms that were established in the Pennsylvanian/Permian and brought to light with Cenozoic erosion. 

The Arbuckle Mountains are almost straight south of Oklahoma City along I-25 north of the Texas-Oklahoma border.  These hills are not really very high, ~1400 feet, there is not much relief—perhaps 600 feet, but they represent a different sort of environment and are popular with visitors. They do have some old rocks and one time on a field trip I was able to visit a large granite quarry in the Tishomingo Granite, ~1.4 Ga.  These rocks are, in turn, overlain by the Cambrian Carleton Rhyolite (seen in the Wichitas), and maybe 15,000 feet of Paleozoic rocks (mostly marine).  The Arbuckles have a similar geological history as the Wichitas and they were both part of the SORS.  The big difference is that in the Wichitas, igneous rocks predominate while in the Arbuckles sedimentary rocks are common, and many are quite fossiliferous.  In addition, the USGS noted “the Arbuckles contain the most diverse suite of mineral resources in Oklahoma: limestone, dolomite, glass sand, granite, sand and gravel, shale, cement, iron ore, lead, zinc, tar sands, and oil and gas; all these minerals are, or have been, produced commercially” (

Honey Creek, originally producing from a spring(s), drops 77 feet at Turner Falls (near Davis) and is probably the most photographed feature in Oklahoma.  Public Domain photo.

The geologic stories of the Wichita and Arbuckle mountains are much too complex for a short article like this.  Unfortunately, I had to use much geological jargon in the paragraphs above, and for this apologize. I did try to insert approximate dates for the geological terms indicated by Ma=millions of years ago. I guess an easy way to look at their history: 1) rifting and/or faulting with accumulation of Cambrian igneous rocks; 2) stable continent and accumulation of mostly marine rocks from  Cambrian-early Pennsylvanian; 3) uplift of the SORS in late Pennsylvanian from tensional forces of the nearby Ouachita Orogeny; 4) erosion in the Cenozoic producing current landforms that were first established in the late Paleozoic.
I have to admit that my visits to the Arbuckle and Wichita Mountains were many decades ago when collecting by rockhounds and students were in much different circumstances.  We simply contacted quarry owners by mail, received permission (especially for non-working weekends), and collected invertebrate fossils to our heart’s content.  In addition, everyone took home a few pieces of granite since the only igneous outcrops in western Kansas were at local cemeteries.  As a result, I really don’t have fossil specimens (in museum collections) or minerals from either the Arbuckle or Wichita Mountains and could not inform readers about any collecting localities. 

In addition, the Oklahoma Geological Survey will allow you to download: copies of Guidebook 26, Geology of the Arbuckle Mountains along I-35, Carter and Murray Counties Oklahoma (Robert O. Fay).  The publication describes the geology at the numerous road cuts along I-35 north of the city of Ardmore; Guidebook 21, Geology of the Eastern Wichita Mountains, Southwestern Oklahoma (Gilbert and Donavan); Guidebook 23, Petrology of the Cambrian Wichita Mountains Igneous Suite (Gilbert); and Guidebook 24, The Slick Hills of Southwestern Oklahoma—Fragments of an Aulacogen (Donovan).  The Slick Hills are the limestone part of the Wichita Mountains located north of the Meers fault.  Go to  Finally, the last time that I traversed through the Arbuckle Mountains the Ardmore Geological Society had installed informative information on a number of road signs.  I presume they are still along the highway.

SOME TRIVIA:  Much land in the igneous rock part of the Wichita Mountains is tied up in the Wichita Mountains National Wildlife Refuge (~60,000 acres).  President William McKinley, in 1901, established the mountains as a “”Forest Reserve.”  It took President Theodore Roosevelt, in 1905, to designate it as a "Game Preserve,” the forerunner of the federal refuge system.  In fact, the refuge is the oldest in the nation.  One of the critical reasons for the establishment of the refuge was to protect endangered species.  Bison, six bulls and nine cows, were introduced in 1907 with stock coming from the New York Zoological Park.  Texas Longhorn Cattle were also introduced to help preserve the “purity” of the strain.  Unfortunately, the original Oklahoma elk subspecies, Merriam’s I think, is extinct so the Refuge imported Rocky Mountain Elk in 1911.  There were also a number of other smaller mammals and birds introduced to this protective island. 

REAL TRIVIA:  Shortly after McKinley’s designation of the Forest Reserve he was assassinated by an anarchist in in 1901.  He was succeeded by his Vice President, Roosevelt.  McKinley was the last President to serve in the Civil War.

AND MORE: An assassin also tried to take down Roosevelt in 1912 as he was campaigning for a third term as President running in the Progressive Party (vernacular—Bull Moose Party). The bullet (32 caliber) went through his steel eyeglass case and 50 pages of a speech (Roosevelt was a realer talker) and three inches of his chest, but did not penetrate his pleura.  Roosevelt gave his speech (Ladies and gentlemen, I don't know whether you fully understand that I have just been shot; but it takes more than that to kill a Bull Moose) with blood staining his shirt and carried the bullet around forever (too dangerous to remove).  
Roosevelt entered the presidency via an assassin’s bullet while another would-be assassin’s bullet ended his campaigning right before the 1912 election and therefore his chance to re-enter the office.  Now, that is real trivia. 

According to the Oklahoma Historical Society (2014) Spanish mining activity existed in the Wichitas as early as the mid-1700’s.  Evidently they were not very successful.  However, in the 1890’s prospectors wandering around in the granite found evidence of these old Spanish mines (and I use the term mine quite loosely).  By 1895 a “gold rush” was on to the Wichitas but, in a similar situation as the Black Hills of South Dakota, the land was part of the Kiowa-Comanche-Apache Indian Reservation.  As usual, miners and settlers put pressure on the U.S. Congress and by 1901 the Reservation was open to settlement and mining (a question—was this why McKinley designated the Forest Preserve?).  In the next 10 years over 2000 gold claims were filed with no one, as far as I can tell, “getting rich,” except some promoters.  A few surface veins were located and holes/mines penetrated into the granite but nothing really paid.

Comancheria, the ancestral home of the various Comanche tribes and bands, occupied much of Texas, Oklahoma, and New Mexico. Perhaps their most famous warrior was Quanah Parker of the Noconis Band.  Parker was the son of Cynthia Ann Parker, a captured Caucasian from Texas, and Peta Nocona.  Most historians, but not all, believe Quanah was born (ca.1850) in or near the Wichita Mountains.      

Hanson, R.E., R.E. Puckett, Jr., D.A. McCleery, M.E. Brueseke, C.L. Bulen, and S.A. Mertzman, 2011, The Cambrian Wichita Bimodal large Igneous Province in the Southern Oklahoma Rift Zone: Large Igneous Provinces Commission

Oklahoma Historical Society, 2014, Gold:  Encyclopedia of Oklahoma History and Culture,

Thomas, W.A., 2011, The Iapetan Rifted Margin of Southern Laurentia: Geosphere, v. 7.

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