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! 
 

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 2^nd 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