Sunday, September 21, 2014

DENVER MINERAL SHOW: 2014

One of the "really big" rock and mineral shows just completed its run in Denver, Colorado, September 12-14 at the Mart Expo Hall.  The theme this year was Agates and as one might expect, the exhibitor cases had specimens from around the world.  For a list of events etc. please see the official website at:  www.denvermineralshows.com.  Like the Tucson events, there are ancillary shows scattered around the city such as Martin Zinn Expositions at the Ramada Plaza Denver Central, the initial offering of the Denver Fine Mineral Show (Denver Marriott West), Denver Coliseum Mineral, Fossil and Gem Show, and others (for example, the fossil show had moved from the Expo Hall to ? well somewhere in the city.  A bead show now occupied space formally used by the fossil group.   A loss in my opinion.).

My schedule only allowed a single day for a visit so I attended the "main show" at the Expo Mart.  The exhibitors had cases of fantastic specimens and the 140+ dealers were well stocked.  The following photos represent some of my favorite cases.  As usual, the reflections of the case glass diminished my already rudimentary photograph skills!

Not all banded quartz is an agate.

The always popular Dryhead Agates.

I liked this arsenate specimen, legrandite from the Ojuela Mine, Durango, Mexico.


Benitoite (top) and neptunite (lower) from the Dallas Gem Mine, San Benito County, California.

The popular amazonite collected by Joe Dorris and Associates from their claims near Lake George, Colorado. The Dorris family are stars in the Prospectors  TV show.


Thundereggs from Oregon.

Wow.



I suppose the eye agates shown above were the most amazing specimens of the Show.
I think this agate is in the Smithsonian. My notes fail me.


Gems from Afghanistan: Beryl var. morganite and spodumene var. kunzite.

My favorite agate---Fairburns from South Dakota.

Zoisite var. tanzanite from Tanzania offered for sale by The Collectors Edge ($65,000).

Rhodochrosite with fluorite from the Sweet Home Mine in Colorado (The Collectors Edge).

Orange-red prismatic crystals of crocoite (Tasmania).

Love this orpiment (arsenic sulfide) and gold ore from Humbolt County, Nevada.

Beryl var. aquamarine from Pakistan.
Something for everyone!

The Expo Hall main exhibit space.  The amazonite display shown above gets prime space on the end cap,

A really nice cut.

Not all agates are banded.  These are dendritic agates.

And finally, the always popular gold panning area.
 

Saturday, September 6, 2014

CONCERNING THE GEOLOGY OF COLORADO



I have received several emails this summer from visitors to Colorado inquiring about geological sights and/or potential mineral collecting areas.  I have tried to answer each, but also have directed writers to web sites of the US Geological Survey and the Colorado Geological Survey, and also suggested a few appropriate search terms for internet search engines.  I really don’t have the energy to furnish specific information (prodigious amounts) for term papers or “how deep do you need to dig for rubies at Ruby Mountain”!  I also furnish web sites for the local BLM and USFS offices, especially for those interested in gold prospecting, amazonite/quartz/topaz digging, and aquamarines from Mt. Antero.  Some television shows seem to indicate semi-precious gems are available virtual everywhere in the mountains of Colorado---just show up and start digging and get rich.  However, if the questions seem reasonable I also suggest visiting the web sites of our many rock and mineral clubs.
I guess all of these questions might indicate that “googlers” are locating my blog site, and therefore I am pleased with the traffic and interest.  A couple of recent inquiries that ended up in my blog spam filter wanted to know what happened to August postings?   Well, the last 5 weeks have been a time of traveling across the Plains and Midwest, picking up a few rocks, and visiting friends.  In addition, and perhaps most importantly, I spent significant time in northwest Ontario floating on the water and slaying the mighty Sander vitreus, also known in the vernacular as walleye.  In my former biology classes I learned the scientific name Stizostedion vitreum.  However, I guess that some scientist decided a new scientific name was in order!
Several years ago I wrote a few paper articles for visitors who attended a rock and mineral show in Colorado Springs.  I have revised these articles and have been sending a copy to readers submitting geology questions.  Therefore, I am transferring this new copy to the blog,  
For the best comprehensive understanding of Colorado’s geology, readers should consider MESSAGES IN STONE: COLORADO’S COLORFUL GEOLOGY written/edited by Vincent Matthews, the State Geologist (since retired), and his colleagues at the Colorado Geological Survey (CGS).  The book was the 2004 winner of the Association of Earth Science Editors Outstanding Book Award.  The numerous book photos are spectacular and the writing superb.  Written for the general public, the book also becomes a reference for the professional.  I originally purchased the 2003 edition but now have the new and revised 2009 2nd edition, with “125 new and/or improved photos [and containing] a new section on mountain building”.  Interested readers may order the book from the Colorado Geological Survey at ~$20 (http://geosurvey.state.co.us/).  This publication allows all readers to better understand both the complex and fascinating geologic history of Colorado.
Accompanying the above book from the CGS is The Tourist Guide to Colorado Geology (also by Matthews) consisting of a map and several related figures and presentations describing the geology and terrains of Colorado (~$10 from CGS).
If readers are deeply interested in Colorado’s minerals, then the “authority” is MINERALS OF COLORADO.  This tome had its first printing in 1961 and is credited to Edwin B. Eckel (1906-1989), a longtime geologist for the U. S. Geological Survey.  In 1997 the Friends of Mineralogy-Colorado Chapter, Inc, with assistance from the Denver Museum of Natural History, published an updated and revised volume that includes “the description of 774 different mineral species from Colorado, … comprehensive locality information, an extensive bibliography,…and 119 color and 26 black-and-white photographs.  The new version is the “result of more than two decades of work” by several noted geologists and mineralogists of Colorado.  The classic is large, coming in at 676 pages in an 8.5” X 11” format; however, the information contained within is comprehensive.  I have spent tens of hours simply perusing the book and noting interesting facts.  It is also my first reference selected when traveling to a new area or inquiring about a Colorado mineral.  Fulcrum Publishing, the original publisher, offers a list price of $150; however, used copies may be purchased from ~$90-100 at online book sellers. 
I suspect that most geology travelers driving to Colorado will have ROADSIDE GEOLOGY OF COLORADO (Chronic and Williams; Mountain Press Publishing; 2002; new at $16, used much less) on their front seat ready for use.  The authors describe the general geology along most of the major highways in Colorado and supply good geologic cross-sections and several nice photos.  Some highway mile posts are noted; however, I would prefer to see additional postings in a revised and newer edition.  This is a great book for every traveler and I would strongly recommend it for rockhounds.  It should also be noted that a few days ago I noted a newly revised 2014 copy (~$24) in a local bookstore,
Advanced hobbyists also should carry the GEOLOGIC MAP OF COLORADO with the most recent edition published by the U. S. Geological Survey in 1979 (www.usgs.gov).   A well known USGS geologist, Ogden Tweto, is listed as the compiler since maps of this scale are the result of individual works by tens/hundreds of individual “mappers”.
Geologic maps show the different ages of surficial rock units superimposed on a base map with placement of rivers, roads and cities.  The uniqueness of the map is due to displayed colors—specific colors represent specific ages of the rocks.  For example, Mesozoic rocks, those belonging to the Cretaceous, Jurassic, and Triassic periods are represented by shades of green.  In addition, faults are always shown and are represented by specific symbols.  On large scale maps, dip and strike symbols, as well as lines representing fold axes, are commonly shown. 
Although this article describes the state map at a scale of 1:500,000, readers should be advised that hundreds of other maps, often at a scale of 1:24,000, exist for Colorado.  The major publishers of all geologic maps are the Colorado Geological Survey and the U. S. Geological Survey.
If visitors are interested in collecting fossils along the Front Range, I might advise that the best collecting sites are in rocks of Cretaceous age, especially the Pierre Shale.  By far the best fossil identification book is a very specific and detailed publication: the July-October 1977 (vol. 14. Nos.3-4) issue of THE MOUNTAIN GEOLOGIST (published by the Rocky Mountain Association of Geologists) and devoted to CRETACEOUS FACIES, FAUNAS, AND PALEOENVIRONMENTS ACROSS THE WESTERN INTERIOR BASIN.  The volume was published as a field guide for the North American Paleontological Convention II.  I had the opportunity to participate in the fabulous field trip that started in Salt Lake City and ended in central Kansas and examined Cretaceous rocks in a variety of environments.  However, the important thing about this book, at least to collectors, is that virtually every invertebrate fossil of Cretaceous age found in the Western Interior is represented with a detailed photograph.  In addition, there are detailed descriptions of major Cretaceous rock units exposed across this vast area.  So, readers will be able to consult a geologic map, locate Cretaceous rocks, and then consult the publication to identify the fossils.
The publication is long out of print; however, consult used book dealers on the internet, especially those specializing in geology books.  I purchased my last copy with a well-spent $15.
One of the reasons that I resettled in Colorado is because of the tremendous variety of hikes that are available for novice walkers to experienced alpinists.  We are fortunate to have two books available for those readers who may be traveling “on foot”: ROCKS ABOVE THE CLOUDS (Reed and Ellis; The Colorado Mountain Club Press; 2009; $13) and HIKING COLORADO’S GEOLOGY (Hopkins and Hopkins; The Mountaineers; 2000; $17).  However, even if you are not a walker/hiker the books help one better understand our wonderful geological scenery. The latter book describes the geological features found along 50 hikes, ranging from “easy” (Garden of the Gods) to strenuous (Mt. Elbert at 14,433 feet---yes, I summited and it was tough for an old guy). All hikes are to areas of geological interest and the book provides explanations for readers of all abilities.
The former, subtitled A HIKER’S AND CLIMBER’S GUIDE TO COLORADO MOUNTAIN GEOLOGY concentrates on the high mountains of Colorado.  The geological descriptions of the various mountain ranges are well stated and each of the state’s 14ers is noted in detail.  The book is small (pocket book size) and well suited for a backpack, but finds room to contain both geological and terrain maps.  My copy is well used as I take it on every trip to the high country.
There are essentially four mineral/rock collecting guides for Colorado.  The oldest guide, and in many ways the best, is COLORADO GEM TRAILS AND MINERAL GUIDE by Richard Pearl.  First published in 1958, the book is very impressive for its detailed descriptions of “how to find the locality”.  I have the 1972 edition purchased at $15 but used copies are widely available from internet book sellers.
Falcon Publishing (A Falcon Guide) has a number of state guidebooks on the market and one is ROCKHOUNDING COLORADO (Kapple and Kapple; 2004; $10 new).  I found this to be of less interest than Pearl’s book since few “exotic” sites are explored and many mineral collecting sites are for common feldspar, mica, etc.  This book might be a better choice for the Pebble Pubs.
James Mitchell has written a number of state collecting guides and rockhound books and I have copies of each.  The Colorado version (GEM TRAILS OF COLORADO) has included good maps for the localities (75) but the book could be greatly improved with some descriptions of the local geology.  Copies of the 1997 edition (Gem Guides Book Co.) are being sold for less than $5 from internet book sellers.
By far the most extensive of the collecting guides is COLORADO ROCKHOUNDING by noted Colorado author Stephen Voynick.  I like the fact that localities are grouped together by counties and that each locality is referenced.  This is the book that I would purchase if only “one” guide is destined for your collection.  New copies are $16 with used books widely available (some at $1).  I believe the latest edition is 1996 so some items seem rather dated.  Perhaps a new and revised edition is on the way?
Whatever guide one chooses please remember that: 1) several described localities are on private land and permission is needed to collect; 2) several localities might be under claim; 3) all vertebrate fossils, and some invertebrates, are protected if they are on federal lands; 4) collecting on state-owned lands (and city and county) is often off-limits so make certain to check with appropriate management agencies; and 5) collecting localities described in guides are often “cleaned out” within a few years.
A really great book appeared on the market in 2012: Geology Underfoot Along Colorado’s Front Range (Lon Abbot and Terri Cook; ~$24 new but less at internet book sellers).  The authors (from the University of Colorado) describe the geological transition from the relatively flat Great Plains to the craggy peaks of Colorado s Front Range as one of North America s most abrupt topographical contrasts.  Covering some 1,800-million-yeas, the geologic story behind this amazing landscape is described as awe inspiring (I agree).   The authors narrate the Front Range’s tale, from its humble beginnings as a flat, nondescript seafloor through several ghostly incarnations as a towering mountain range. The book has 21 chapters, each leading readers to easily accessible stops along the Front Range’s highways and byways.  Visitors at these described stops will walk in the footprints of dinosaurs who roamed the floodplains and beaches that once covered the Front Range; look for diamonds in rare, out-of-the-way volcanic pipes; learn how Pikes Peak developed from molten magma miles below the surface: and walk the Gangplank, a singularly important plateau for nineteenth-century westward expansion.
Geology Underfoot makes for a fantastic read and I could not lay the book down until finished.
And finally, I mention two books that focus on the general geology of Colorado.  GEOLOGY OF COLORADO ILLUSTRATED (Foutz; personally published; 1994) describes the geology of Colorado from a locational perspective.  That is, geologic descriptions of major features, such The Denver Basin, The Grand Mesa, The Dinosaur Corner, etc., are described.  Each location has a generalized geologic map and several photographs (in black and white). With a publication date of 1994/1999 the book is getting somewhat outdated.  New copies list at $18 with used prices at $6 or less.
GUIDE TO THE GEOLOGY OF COLORADO (Taylor; Cataract Lode Mining Company; 1999), a book that is well-written and used by both serious students of geology and recreational rockhounders.  Profusely illustrated with color photographs and printed on glossy paper, the book tackles the geologic time scale and then describes the geology of numerous localities of interest.  New copies (perhaps not currently available) come packaged with a general geological map of Colorado.  Used copies are available for $16 or less.
So, travelers to Colorado have a variety of publications available for their perusal and possible purchase—the above list is only a starter!  And remember, local libraries are excellent resources for browsing.  If copies of sought after books are not in the book catalog perhaps you could order the books via Interlibrary Loan.
A Disclaimer: this article, and recommendations contained within, are solely the opinions of the author and do not imply an endorsement from any organization or individual.  And, if you visit our state, make certain not to trespass.
People should educate themselves - you can get a complete education [in the public library] for no money.  Ray Bradbury

Wednesday, July 30, 2014

ROADTRIP: OKLAHOMA CENTRAL PLAINS AND PANHANDLE



My initial "Oklahoma Blog" centered on the eastern one-third of Oklahoma, home of deciduous trees, Mississippian and Pennsylvanian rocks, coal mines, a coastal plain, large lakes, the Ouachita and Ozark Mountains, and the lead-zinc mines.  In this Blog I move further west where the middle third of the state is dominated by exposures of late Pennsylvanian and Permian rocks, many of which are red in color.  The Panhandle region has exposures of dinosaur-containing Mesozoic rocks along with a Tertiary cover and a few basalt flows.  Interrupting this logical sequence of rocks are two interesting “mountain” regions—the Arbuckle Mountains south of Oklahoma City and the Wichita Mountains in the southwest near Lawton---subjects for my next Blog.




Geologic map of Oklahoma (from Oklahoma Geological Survey).  Note the light blue streak (Permian) trending north-south through the state.

 

Physiographic regions of Oklahoma (courtesy Oklahoma Geological Survey).  A the Arbuckle Mountains, W the Wichita Mountains, RB, the Permian redbeds, HP, the High Plains.  Compare with map above.

A more detailed province map of central Oklahoma (courtesy of Oklahoma Geological Survey).

To better understand the geology and related landforms of Oklahoma, readers should keep in mind above maps.
 
The sandstone cuestas (Spanish for cliffs) region has gently dipping, to the west, sandstone layers protecting underlying, slope-forming shale layers.  The sandstone of the province is late Pennsylvanian in age and was formed as flowing rivers carried sand and other sediments into deltas and estuaries of  an ocean.  These sandstone hills are quite scenic with a somewhat distinct flora and fauna and extend into Kansas as the Chautauqua Hills.  The dipping beds of the cuestas are associated with the large Ozark dome to the east.  I have collected some nice tree-fern fossils in the northern reaches of the province but mostly I just visited the area for the scenic beauty and camping, noting the old-growth forests of post oak and blackjack oak with blooming redbuds in the spring.

In Kansas, the Flint Hills are one of the major physiographic provinces in the state (trending north-south) and provide a unique landscape of native tallgrass prairie in a rocky and hilly terrain with major relief (at least for the plains states).  In Oklahoma this province is known as the Limestone Hills (also The Osage or the Limestone Cuestas) and only extend about one-third of the way south.  The Flint Hills/The Osage have marine early Permian rocks exposed and are quite fossiliferous.  I have not collected in the Osage but have pulled hundreds/thousands of fossils from the Flint Hills in Kansas.  For 20 plus years I took my undergraduate invertebrate paleontology class to the Flint Hills and students routinely collected over 100 different species from Permian rocks.

Cartoon showing configuration of continents at the end of the Paleozoic Era.  Note how Africa and South America collided with North America and produced the Appalachian and Ouachita Mountains.  Public Domain map.

The later Permian represents the end of the great Paleozoic seaway in the U.S. where marine waters that had covered parts/most of the continent since the late Precambrian were receding and drying.  Plate activity had moved continents world-wide so that a single large continent, Pangaea, was formed and, except for continental margins, marine waters receded from the (current) North American continent.  The later Permian represented the culmination of the Appalachian-Ouachita Orogen where Gondwana was attached/sutured to (current) North America.  As the Permian seas were drying and receding the continent experienced restricted circulation waters and widespread deposition of halite and other “salts” and gypsum.  In addition, wind and fluvial (stream) deposits containing grains of iron-rich minerals later “rusted” and created the color in the widespread redbeds trending north-south through the center of the state.  As these beds extend north into Kansas they are known as the Red or Gyp Hills.  I have examined the gypsum, anhydrite, and dolomite but found them rather uninteresting as mineral specimens and “left them in place.” 

Now, I have to admit that my experience with the central Oklahoma redbeds essentially has been driving I-35 south to the Arbuckles or Texas Cretaceous!  About the only prospecting accomplished has been to look for the barite roses.  Of  course, I suppose these concretions are the best-known mineral in this part of the state.  
  
Barite rose collected near Norman from Permian Garber Formation.  Width of left single rose ~3.5 cm.

There are several instances where minerals, mostly calcite, barite, and selenite gypsum, have formed clusters of crystal “roses” or sand crystals.  In some case the roses are formed from “pure” minerals, with maybe an encrustation of sand grains, such as the selenite roses (Desert Roses) from St. David, Arizona (see Blog Feb. 4, 2013).  However, in parts of northwestern Nebraska the selenite roses have been replaced by chalcedony.
In other cases the mineral solution carries along sand-size grains from the host rock as inclusions.  London (2008), in an article in The Mineralogical Record, noted that “roses are mineral specimens, not rocks, because the shapes of rocks are indeterminate, whereas the shapes of minerals are determined by a combination of forms and habits derived from the interplay of crystal structure and environment of growth.”  Each of the petals of the rose are individual barite crystals.  The Oklahoma roses are due to the “intergrowth of crystals of barite…into a cluster of divergent blades… The rose-like concretions incorporated the iron-stained quartz sand grains and thus acquired the red color of the host Garber Sandstone” (Tulsa Geoscience Center, 2012).  The Oklahoma Geological Survey (London, 2009) noted that “the best explanation for the roses is that deep basinal groundwater containing barium and reduced sulfur species (sulfide) migrated upward along fractures and porous layers into the Garbar Sandstone.  Upon reaching an aerated region, the sulfur in the groundwater was then oxidized from sulfide to sulfate, leading to the precipitation of barite.”

Barite roses were designated as the official “State Rock” in 1968.  It seems unfortunate that no mineralogist (or so it seems) told Governor Bartlett and the legislature that barite roses are minerals, as opposed to rocks.  But, life goes on!

In Kansas, the red to orange barite roses are similar except they have been collected from the Cretaceous Kiowa Formation (see Blog July 23, 2013) derived from barium-rich solutions in the underlying Permian rocks.

Barite Rose collected many years ago near the hamlet of Bavaria, Kansas, in Cretaceous rocks. Width ~6 cm.

Calcite sand crystals are similar to the barite roses except the form takes on the shape of calcite crystals.  I suppose the most famous locality for collecting these latter crystals has been Rattlesnake Butte in South Dakota (now off-limits see Blog Jan. 9, 2014) although some crystals have started to come from Wyoming (see Blog Dec. 17, 2011). 

The further west one goes in Oklahoma, the less time I have spent in the region other than traveling south to the Wichita Mountains or to southwestern Texas where my son attended a university.  A long time ago (my favorite phrase) I did take my students to: 1) Alabaster Caverns State Park; and 2) the Great Salt Plains.  The cave is formed in Permian age massive gypsum and is a solution cavity.  In my home state of Kansas a few miles to the north, there are large sinkholes such as Big Basin that are related to subsurface dissolution of similar age gypsum and halite.  At one time, before collapse, a large natural bridge near Sun City was 35 feet wide, 55 feet long, and 12 feet above stream level.  In addition, there are at least 117 gypsum caves in Barber County (Kansas Geological Survey, 2013). 
The second place that we visited was the well-known Great Salt Plains near the Arkansas River to dig and collect selenite gypsum crystals--there is both a state park and a federal wildlife refuge and collecting is on the refuge and hours/days etc. are posted.  Check ahead before you drive to collect!
Big Basin is a sinkhole  south of Dodge City, Kansas.  Permian halite and gypsum beds in the subsurface have dissolved allowing the surficial Ogallala Formation to collapse.
As it appears to me, the salt plains are essentially a playa with incoming fresh water, at times, but without an outlet.  The original source of the salt and gypsum are beds in the underlying Permian rocks---as noted above, the great Paleozoic seaway was receding and drying and evaporation of brine waters left behind a number or different minerals.  In the playa, the saline- and gypsum-infused groundwater is usually a few inches to to few feet below the surface.  If the groundwater reaches the surface for a short duration but then evaporates a crust of halite forms while the gypsum crystals form below the surface. These selenite crystals at the salt plains are sort of a chocolate brown to orange color due to minor amounts of iron oxide used as a coloring agent.  What makes the crystals unique is that they have included tiny sand grains and these grains are in the shape of a hourglass!  Some crystals are covered by a thin layer of sand while others are quite transparent and the included sand grains are clearly observed.  According to all references I could locate, this is the only locality in the world where this hourglass inclusion occurs.  I don’t have the slightest idea “why” and it appears that other geologists are also “stumped” at the shape of the inclusions.  At times the crystals are solitary, sometimes they are twinned (penetration twins common), and many times are in clusters. A gazillion of these crystals have been collected since they are “for sale” in virtually every rock/mineral shop, and in the rock and mineral shows.  But they are also fun to collect if you don’t mind getting a little muddy during the process. 

Penetrating twin hourglass selenite with sand inclusions.  Length ~4.0 cm.  In 2005 Oklahoma designated hourglass selenite as the official State Crystal.

Along the Cimarron and Canadian Rivers a hummocky terrain of both grass covered (stabilized) and active sand dunes is found.  Most of the dune fields are on the north side of the rivers as a southern wind blows sand- and silt-size grains from the current alluvium and the older terrace deposits.  These dune fields are similar to the large fields on the north side of the "big bend" of the Arkansas River.  
I have always had an interest in history, and especially of western U.S history between ~1800 (Lewis and Clark) to ~ 1890 (Wounded Knee).  This was a time of great conflict between representatives of the federal government and the Native Americans.  Since I grew up in Ottawa County Kansas I have been particularly interested in the summer of 1868 when Southern Cheyennes and some of their allies raided settlements along the Saline and Solomon rivers (I grew up fishing in these rivers) killing several Caucasian settlers.  Partially as a result of these raids General Phillip Sheridan, Commander of the U.S. Army’s Department of Missouri, an area of over a million square miles between the Rocky Mountains and the Mississippi, decided to conduct a winter campaign against the “insurgents.”  In this manner he hoped to destroy food stores and horses along with people and housing at a time when the Native Americans were usually semi-permanently camped for the winter.  In late 1868 Sheridan sent Lt. Colonel George A. Custer on a winter mission to subdue the Southern Cheyenne in western Oklahoma.  At the ensuing battle or massacre (I will not get into that argument) on November 27, 1868, Custer destroyed the village of, and killed, the Cheyenne Peace Chief Black Kettle at an encampment along the Washita River in the redbed plains of far western Oklahoma.  If readers ever get a chance, take a side trip and visit the national monument.  

About where the Panhandle “hooks on to” the main segment of Oklahoma the Plains Border section of the Great Plains Physiographic Province ends and the large High Plains section begins.  At one time in the late Tertiary the Ogallala Formation (Group) extended from the Rocky Mountains (the source for its sediments) eastward to the Missouri River and beyond.  However, uplift to the west, and erosion by rivers on all sides, has essentially left the High Plains as an island, one that is capped by the Ogallala Formation.  Today the High Plains extend from the Pine Ridge Escarpment along the South Dakota-Nebraska border south to the breaks at the Edwards Plateau in Texas.  The western boundary is situated at the eroded breaks along the mountain front (such as the Colorado Piedmont).  In the east the formation feathers and thins and the High Plains end.  Most people know about the High Plains as being the source of the rapidly depleting Ogallala Aquifer.  Exposures of the Ogallala Formation are common in the Panhandle. 
 
A very unique geological area is located in the far western Panhandle of Oklahoma and much geology is preserved in Black Mesa State Park and the surrounding area along the Cimarron River where rocks from the Triassic to Recent are well-exposed.  Triassic and Jurassic rocks in the Great Plains are relatively rare east of New Mexico and Colorado as are Cenozoic volcanics.  However, a nice section of of the Triassic Dockum Group and the overlying Entrada and Morrison Formations of Jurassic age crop out in the area.  Of additional interest are the remains of dinosaurs, both body fossils and ichnofossils (dinosaur tracks), from the Morrison.  Most people with even a slight interest in natural history usually associate dinosaur fossils with places like Dinosaur National Monument and the Cleveland-Lloyd Quarry in Utah, and Canon City and Dinosaur Ridge in Colorado.  However, an Oklahoma geologist by the name of Willis Stovall collected thousands of dinosaur bones from the Morrison around Black Mesa in the late 1930’s and early 1940’s.  Today most of these fossils reside in the Sam Noble Oklahoma Museum of Natural History.

One particular dinosaur collected by Stovall from near Black Mesa was designated in 2000 as the State Fossil of Oklahoma.  Saurophaganax maximus is a large theropod (meat-eating) maybe 50 feet in length and 17+ feet tall.  It is most likely related to the allosaurs, the dominant theropods of the Morrison.  A cast of a front claw is shown below.


Terminal phalanx or claw of Saurophaganax maximus (cast replica).

I once participated in a field trip to the area, mainly to examine the exposures of Cretaceous rocks.  This section is very similar to the Cretaceous rocks in Kansas, the big difference being the aerially widespread exposures in Kansas compared to quite limited outcrops in Oklahoma.  The oldest Cretaceous units are the Cheyenne Sandstone, a fluvial sandstone (mostly), overlain by the marine Kiowa Shale.  The latter formation is quite interesting is that it contains a “southern” assemblage of invertebrate fossils.  That is, marine waters invaded the continent from the south and the resulting rocks contain fossils normally associated with Gulf Coast Cretaceous rocks in Texas. 

Marine waters then retreated south and the mostly non-marine (wind, stream, delta, estuary) Dakota Formation was deposited.  Some units in the formation contain dinosaur tracks (similar to Dinosaur Ridge in Colorado).
The widespread Western Interior Seaway (WIS) is represented in Oklahoma by the Graneros and Greenhorn Formations (calcareous shales and limestones) overlying the Dakota.  Invertebrate fossils such as coiled ammonites and straight-shelled baculites, along with inoceramid bivalves, are abundant.  The WIS had marine waters transgressing from both the north and the south and the resulting northern fauna is completely different from fossils found in the Kiowa Shale.


Image of Mesa de Maya and Black Mesa, Colorado, New Mexico and Oklahoma.  Image © Google Earth.

One of the best known structures in south-central/southwestern Colorado is the Raton Mesas starting near Trinidad and continuing eastward along the Colorado-New Mexico state line where thick (~800 feet) late Tertiary basalt flows (~3.5--9.0 Ma) cap the Poison Canyon Formation (Tertiary: Paleocene) and hold up the topography.  The area, including Barella Mesa and Johnson Mesa, is often referred to as the Raton-Clayton Volcanic Field since the basalt extends as far east as Clayton, New Mexico.  Near Trinidad, Fishers Peak (9626 feet) is the highest point in the United States east of I-25.  Further east on the plains, “near” Tobe, and Walt’s Corner, Colorado,  is an isolated, but related, mesa termed Mesa de Maya where 400-500 feet of basalt cover the Ogallala Formation at an elevation of around 6500 feet.  The Mesa continues south and eastward as Black Mesa and actually extends into the Oklahoma Panhandle where at 4973 feet it is the highest point in Oklahoma.  Suneson and Luza (1999) believe the age of the capping basalt flow at Black Mesa is ~5 Ma.

For additional reading see:
Publications, many available as PDF files, of the Oklahoma Geological Survey at: www.ogs.ou.edu.
Neil Suneson, 2010, Petrified Wood in Oklahoma: The Shale Shaker, v 60, no.6.
Common Fossils of Oklahoma, Sam Noble Museum:  www.commonfossilsofoklahoma.snomnh.ou.edu
Oklahoma Crystal Collecting: www.brightok.net/~rockman/

REFERENCES CITED

Anonomous, 2013, Red Hills: Rocks and Minerals: Geofacts, Kansas Geological Survey. 

London, D., 2008, The Barite Roses of Oklahoma:  the Mineralogical Record.

London, D., 2009, The Barite Rose; State Rock of Oklahoma: Oklahoma Geological Survey.

Tulsa Geoscience Center, 2012, Barite Rose: Our State Rock: www.tulsageosciencecenter.org

Suneson, N. H. and K. V. Luza, 1999, A Field Trip Guide to the Geology of the Black Mesa State Park Area, Cimarron County, Oklahoma: Oklahoma Geological Survey Open-file Report OF4-99.