On this page		Subsections
Introduction		Link Types Units and Terminology Limited Warranty
	Maroon Bells
Photojournal Index		Featured Locations Coming Attractions
	Monument Canyon
Visual Aids
	Western US
Sources
	Field trip, stop 3
Acknowledgements		GSA Meeting and Field Trip, Denver 2002 GSA Publications Special Thanks
	Co-dependents
General References

Last modified 01/03/05

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Introduction

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Painted Wall, Black Canyon of the Gunnison

Her high mountains and deep canyons leave no doubt that Colorado's beauty is far more than skin deep. In fact, it's four-dimensional if you count time, and of course you must.

Over the last 1.8 Ga (billion years), many seascapes and landscapes have played out in the place we call Colorado—from deep ocean trenches to shallow tropical seas to beaches and offshore bars to vast desert dune fields to arid tidal mudflats, from lush redwood forests to volcanic moonscapes, from tropical volcanic islands to high glacier-carved inland mountains. The rocks now exposed at the surface in Colorado provide an incomplete but still fairly readable record of its physical journey through deep time. The otherwise inaccessible rocks glimpsed in road cuts, tunnels, mines and wells help geoscientists flesh out the story. 

This website celebrates just a few of the many stories Colorado's rocks have to tell. Recounting them online is an exercise in geo-journalism, a reporting of the what, where, when, how and why of physical Colorado in a regional context while featuring points of particular interest in the Colorado landscape. (Occasionally, the who figures in as well.) If my words and photographs impart even a hundredth of the wonder and fascination that a writer like ^John McPhee or a painter like ^Maynard Dixon can stir, I'll have done a decent job. 

With a subject as four-dimensional as geology, you can never have too many diagrams and photographs. I wish I had many more, but my permissions, time and artistic skills go only so far. Most of the diagrams shown here come with permission from ^Geological Society of America publications or from online public domain ^US Geological Survey  and NASA resources.

Like Colorado itself, this site is a work in progress. The personal geologic vignettes and photographs gathered here come from day trips in and around the Denver area, family vacations in Colorado, geologic field trips guided by professionals, and geologically-oriented road trips around the state in the company of my good friend and fellow reader of rocks, John Barr. I plan to add more material as my travels widen. The supporting "groundwork articles" draw from many resources, some of which are acknowledged below.

Link Types

Mount Evans from Denver

This site relies heavily on internal and ^external links opened in the same browser window, and also on %selected internal and external pages opened in a new browser window. 

After clicking an internal or ^external link, use your browser's [Back] button to return to the internal page where you left off. Thumbnails with no border behave the same way. 

Links prefixed with a percent sign "%" lead to internal or external pages opened in a new browser window. The same is true of thumbnail images with a heavy green border. If left open, the same new window will be used for all subsequent "new window" links.

Terminology and Units

Albert Einstein once said something like, "When you fully understand an idea, you can explain it in simple terms," but he never said it would be easy. I've done my best to write by that creed, but my understanding has limits, and geoscience jargon does afford a certain economy of word, thought and mental image. I've made an effort to introduce important terms along the way, but in the interest of text flow and time (mine), I've often assumed an unrealistic familiarity with geologic lingo and timescales—at least for most potential visitors. 

If you find yourself in need of definitions or time frames, I heartily recommend the online geologic glossaries and timescales listed on the search page. This site follows the 1999 ^Geological Society of America timeline.

Striking the proper balance between simplicity and nuance, overview and detail, lumping and splitting is always a challenge. In a primarily observational science like geology, juggling the known with the conjectured invites even more verbiage. I've never been known for brevity, but I've done the best I can to be fair to the data without losing the mountains for the rocks.

Time and Distance Units

Throughout this site, deep time units are expressed as follows:

The last two examples illustrate a potentially confusing ambiguity in the way these units are used here and in most geology texts. Logically, a stated time may represent a duration (the 30 Ma in the second example) or a specific time in the past (the 10 Ka in the last example). Feel free to add "ago" to these time units as context requires.

For now, distances appear in both English and metric units at my convenience. Eventually, they'll all be metric.

Limited Warranty

The author at Roxborough State Park, 2003

The information presented here is accurate and current to the best of my knowledge. When I first undertook this site in late 2001, with a view toward learning Colorado geology as quickly as possible by writing about it, I was an avid amateur geologist with 25+ years of geology reading and professionally- and self-guided field trips under my belt — all primarily in California. As of January, 2005, however, I'll be a graduate student in geology at the ^Colorado School of Mines.

My research for this site has been careful and reasonably complete, but all errors and misconceptions are mine. If you spot one, or any other opportunity for improvement, please let me know at colorado@cliffshade.com.

Thanks for stopping by.

Jeremy McCreary, MD

Denver, CO

Top    Page Index

Photojournal Index

Skip to Acknowledgments

Most of the photojournals linked on the left below focus on a particular Colorado destination of geologic interest. They include one or more sections of introductory text followed by a photo gallery also divided into sections. The text and gallery sections are linked separately in the table below. 

Many of the photojournals also include material on points of interest encountered on the way that may or may not pertain to the main destination. You'll find these side attractions included among the gallery links.

Photojournal		Text Sections	Gallery Sections
Black Canyon of the Gunnison Simply Extraordinary		Simply Extraordinary How To Make a Black Canyon	Hotchkiss and Crawford Black Canyon of the Gunnison National Park, North Rim West Elk Mountains Somerset—Coal Country
	Painted Wall
Colorado National Monument A Taste of the Colorado Plateau		A Taste of the Colorado Plateau	Colorado National Monument Book Cliffs Grand Junction
	Monument Canyon, Colorado National Monument
Dinosaur Ridge and Vicinity A Tale of Two Uplifts And a Sea Dragged In By the Thrust Belt Next Door		A Tale of Two Uplifts And a Sea Dragged In By the Thrust Belt Next Door East To West, Young To Old The Golden Fault	Dakota Hogback at Dinosaur Ridge Dakota Hogback Variations Red Rocks Park Dinosaur Ridge—Morrison Fm Dinosaur Ridge—Dakota Sandstone North and South Table Mountains Green Mountain I-70 Road Cut and the Front Range Foothills
	Dakota Hogback, looking south
Elk Mountains A Range of Many Colors		A Range of Many Colors Elk Range Evolution	McClure Pass Mt. Sopris Castle Creek Valley Cathedral Lake Maroon Bells
	Maroon Bells
Garden of the Gods A Mad Dash From Aspen To Colorado Springs		A Mad Dash From Aspen To Colorado Springs	Independence Pass and the Sawatch Range Twin Lakes and Lake Creek Valley Upper Arkansas River Valley (discussed but not shown) Southern Mosquito Range Wilkerson Pass and South Park Florissant Fossil Beds National Monument Garden of the Gods Park Pikes Peak
	Kissing Camels, Garden of the Gods
The Gore Range, the Lower Blue River Valley and the Williams Fork Range More Complicated Than They Look		Faults and Glaciers	Gore Range Buffalo Mountain Buffalo Assault, September, 2002 Williams Fork Mountains and Thrust Lower Cataract Lake (coming)
	Red Peak over the shoulder of Buffalo Mountain
Mount Evans And Other Giants of the Front Range		Towering Above the Mile-High City Mount Evans Batholith Idaho Springs- Ralston Creek Shear Zone	Mount Evans Longs Peak Pikes Peak Idaho Springs-Ralston Shear Zone
	Mount Evans from Denver
Tenmile Canyon and Range Post-Laramide Creations of the Rio Grande Rift		Tenmile Canyon Tenmile Range An Untidy Divide	Tenmile Canyon Northern Tenmile Range
	Peak 1, Tenmile Range

Coming Attractions

• Front Range Medley

• San Juan Mountains

• Black Canyon, South Rim

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Visual Aids

Geology plays out in four dimensions. To get a grip on at least two of them, I strongly recommend attempting to digest this site with some visual aids in hand.

• Geologic Highway Map and Shaded Elevation Map of Colorado (2002 revision)—none of the few online maps I've found can match it. Since repeated map study pays handsomely, I keep a copy in each car and another in my briefcase.

• Colorado Recreational Road Atlas, Pierson Guides, 1991 (available at ^MAPSCO, Denver, CO), or some other good shaded relief road map.

• Physical Earth— for a global context in both space and time, dig out this 1998 ^National Geographic Society insert map if you happen to take the magazine. If not, try opening UNAVCO's ^Jules Verne Voyager online map server in a separate browser window.

• Andrew Taylor's 1999 Guide to the Geology of Colorado—  the many excellent outcrop photos and the accompanying annotations are the next best thing to being there.

• A globe with relief, especially for the Earth At Work article. Flat maps can be very misleading when it comes to plate relationships. Nothing beats seeing them in the round. Most plate boundaries are readily identified from the relief alone.  

I've included as many illustrations as I can get my hands on legally, but the site could obviously use many more.

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Sources

Colorado's story continues to evolve—both in the rocks and in the minds of geoscientists. Her profound beauty, her spectacular exposures and her tantalizing puzzles have long attracted some of the best minds in the business, but her many overprinting processes have left a tangled web indeed. Many chapters in the story remain controversial or frankly unknown, and some just beginning to yield to investigation may take decades to tease out.

I've assembled the "big picture" presented here as best I can from a number of sources, including

• the references cited below, in other articles (particularly The Earth at Work) and on the home page, 

• materials and talks presented at the ^2002 Geological Society of America (GSA) meeting in Denver, including six exciting sessions devoted to the Rocky Mountains.

• a seminal pre-meeting GSA field trip to the Front and Sawatch Ranges entitled Formation, Reactivation, and Evolution of Proterozoic Shear Zones in the Colorado Rocky Mountains: From Continental Assembly to Intracontinental Orogeny, ably led by Colin Shaw, Karl Karlstrom and Michael Williams. 

• on-going personal communications with geoscientists working in Colorado and like areas

Over the years, many kind geoscience mentors have contributed to the understandings offered here, as I've acknowledged elsewhere, but the misunderstandings here are all mine.

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Acknowledgements

Skip to General References

Matt & Casey

Over the last 25 years, I've had the good fortune to live in two hotbeds of geoscience talent—California's San Francisco Bay Area and Denver, Colorado. I first realized how eager most geoscientists are to share their knowledge and enthusiasm with interested laymen in 1982, when I timidly joined the Peninsula Geologic Society, a veritable "who's who" of West Coast earth science drawn primarily from the Stanford faculty and the USGS Western Division headquarters in Menlo Park, CA. At monthly meetings and on many a field trip, these early mentors gave me a solid leg up on field geology that no book could impart. Special thanks go to the late Clyde Wahrhaftig for allowing me to assist in his Marin Headlands field work, for putting up with my ceaseless questions, and for helping me learn to make some sense of the aptly-named "trash-can geology" of coastal California. At 80, Clyde could still out-hike me, and I was 30 something and in very good shape at the time.

My good luck with the Peninsula Geologic Society emboldened me to try tapping into the local talent once again on moving to Denver in 2001, and I've not been disappointed. Conversations and field trips with many geoscientists met through the ^Geological Society of America, the  ^Colorado Scientific Society, the ^Colorado School of Mines, the ^Rocky Mountain Association of Geologists and this web site have been invaluable. I'm particularly grateful to Warren Hamilton, Bob Raynolds and Vince Matthews, as noted below.

Geological Society of America Meetings and Field Trips, Denver, 2002 and 2004

When the Geological Society of America (GSA) annual meeting came to Denver in 2002, a year after our move to Colorado, I couldn't resist. A 2-day pre-meeting field trip focused on Colorado's Precambrian history turned out to be the perfect setup for the talks ahead, which in 2002 included no less than 6 half-day technical sessions devoted to the Rockies. I couldn't have asked for a better leg up on the current state of Colorado geology, but even more gratifying was the opportunity to meet and talk with many of the leading workers in the Southern Rockies. 

When the meeting came back to Denver in ^2004, I signed up for two field trips, both to the northeast flank of the Front Range — an area at the heart of a long-standing and deep-seated controversy regarding the structure and tectonic style of the entire Laramide orogeny. There were fewer Rocky Mountain talks than there had been in 2002, but 

2002 Shear Zone Field Trip

Field trip, stop 3

I'm still patting myself on the back for signing up for a seminal pre-meeting field trip to the Front and Sawatch Ranges, ^Formation, Reactivation, and Evolution of Proterozoic Shear Zones in the Colorado Rocky Mountains: From Continental Assembly to Intracontinental Orogeny, ably led by Colin Shaw, Karl Karlstrom and Michael Williams. As the GSA meeting to follow unfolded, I came to realize that the field trip roster amounted to a current "who's who" of Colorado geology — and I'd managed to pick the brains of just about everyone there! All proved to be gracious and enthusiastic teachers, but I'm especially grateful to

• my field trip vanmates (particularly Bill Nesse, Tom Moeglin, Tom Plymate and Amanda Tyson) for helping me put the stops in context, for shaping my current understanding of Colorado's Precambrian and Laramide past, and most of all, for resisting the urge to throw me out

• Chuck Chapin of the New Mexico Institute of Mining and Technology for helping me wrap my head around Colorado's Tertiary magmatism and the importance of climate change in the geologic record

• the entire Australian geoscience contingent—particularly Peter Betts and David Giles—for familiarizing me with the many compelling Paleoproterozoic and modern analogs to Colorado's past to be found in and around Australia

• Andy Kerr of the Newfoundland & Labrador Department of Mines and Energy and Pat Bickford and Barbara Hill of Syracuse University for making sure I took in all the important field observations along the way

• Eric Nelson of the ^Colorado School of Mines for his tutelage at the rocks and for hooking me up with the geologically-oriented ^Colorado Scientific Society.

2004 Front Range Field Trips

To a student of the Rockies in general and the Front Range in particular, the ^2004 GSA field trip offerings presented some tough choices. There were at least four tasty Front Range trips, but one before and one after the meeting were the best I could do. I finally settled on two that brought somewhat conflicting interpretations to the northeast flank of the Front Range between Fort Collins and the Wyoming line. 

A wealth of observable structural and tectonic detail makes the northeast flank a natural focal point in ongoing debates surrounding the kinematics and dynamics of the Front Range and indeed of the Laramide orogen[] as a whole. (For the uninitiated, kinematics studies the way things move — direction, velocity, timing — without regard to driving forces; why they move the way they do is the purview of dynamics.) Along its southern and central segments (south of Boulder), the high and steep east flank of the Front Range drops precipitously into the deepest portion of the Denver Basin along largely inferred high-angle reverse faults (among them the Golden Fault) with at least 25,000' of accumulated throw. In contrast, the range front basement north of Fort Collins is broken into a jostled array of large and small blocks that generally stair-step down to the east into a much shallower northern lobe of the Denver Basin. Between Fort Collins and Boulder is a transition zone characterized by fewer blocks and a basin floor of intermediate depth. 

Vince Matthews' superbly illustrated pre-meeting trip entitled "Overview of Laramide Structures along the Northeastern Flank of the Front Range" focused on kinematics — specifically, on evidence for differential uplift of the northeast flank's basement blocks along steep (presumably reverse) northeast- and northwest-trending faults. We visited many striking examples of Paleozoic and Mesozoic sedimentary strata draped in ductile fashion over variably uplifted basement blocks separated by brittle faulting. The trip ended at a spectacular exposure of the southern edge of the large, east-dipping Blue Mountain block along the north side of Dry Hollow Creek, west of Berthoud. A markedly attenuated Fountain Formation monocline stretched over the edge of the basement block added weight to Matthews' view of the sedimentary strata as so much "melted cheese" covering the shattered basement of the northeast margin of the Front Range block. 

Eric Erslev's post-meeting trip entitled "Laramide Horizontal Shortening in the Rockies: Faulting and Folding in Oblique Backlimb-Tightening Structures of the Northeastern Flank of the Front Range, Colorado" presented the case for regional east northeast-trending horizontal shortening as the main driving force for northeast flank structure, Front Range uplift and for Laramide deformation in general.

Although colleagues often portray Matthews and Erslev as respective spokesmen for the long-opposed "verticalist" and "horizontalist" camps of Laramide dynamics, I came away from the 2nd trip thinking that the Laramide may well be big enough for both of them. Erslev's orogen-scale horizontal dynamics reconcile easily with Matthew's local high-angle kinematics if one steps back and views the northeast flank as a large high-angle backthrust belt related to limb-tightening as the eastern margin of the Front Range block thrust eastward over Denver Basin sediments during the Laramide. Could their perceived disagreement turn out to be nothing more than an artifact of focus and scale? Six wise men long famous for their early elephant observations might find grounds for optimism here.

Luckily, the GSA's Field Guide 5: Field Trips in the Southern Rocky Mountains, USA, edited by Eric P. Nelson and Eric A. Erslev, contains detailed field guides for the two trips I was most reluctant to pass up: Karl Kellogg's "The Colorado Front Range: Anatomy of a Laramide Uplift" led by Karl Kellogg, Bruce Bryant and John C. Reed, and "Continental Accretion, Colorado Style: Proterozoic island arcs and backarcs of the central Front Range" led by Lisa Rae and Thomas R. Fischer. Charley Haddox and I have been working through them as weekend time and winter weather permit.

GSA and USGS Publications

Jeanette Hammann at ^Geological Society of America headquarters in Boulder deserves a tip of the hat for helping me arrange permissions to use graphics from two superb GSA publications, Geology and GSA Today. Since my text would have had a hard time standing without these invaluable visual aids, I'm also grateful to the GSA for its generous permission policy.

Among the many authors of USGS public domain publications whose knowledge and graphics went into this effort, explicit thanks go to W. Jacqueline Kious and Robert Tilling, authors of ^This Dynamic Earth: The Story of Plate Tectonics for all the excellent diagrams, maps and photos. This site would have been graphically barren without them.

Special Thanks

My deepest thanks go to ^Warren Hamilton,  Distinguished Senior Scientist in geophysics at the ^Colorado School of Mines, for his generous and patient mentoring on geodyanmics following an initial e-mail exchange regarding his thought-provoking 2002 GSA meeting talk later published as ^An Alternative Earth. His capacity for questions is exceeded only by the quality of his answers. Warren's advanced my understanding of global and local tectonics by orders of magnitude. I have no doubt that his overarching view of the planet and its workings and his dogged focus on the observations (as opposed to the stories told about them) will guide the way forward in geodynamics.

John Barr

My true friend and geology buddy John Barr wins the stamina award hands down for listening to me puzzle out overlook after outcrop on our many, many outings together—and especially for poking holes where required. His interests range wide, his love of nature runs deep, and his ability to resist glazing over is exceeded only by that of my dogs, who don't even seem to know how. I enjoy John's company and conversation immensely.

According to an old Chinese proverb, when you're ready to learn, your teacher will appear. To my great good fortune, two excellent teachers appeared — ^Bob Raynolds, research associate and consulting geologist attached to the ^Denver Museum of Nature and Science and its exciting ^Denver Basin Project, and ^Vince Matthews, current director of the ^Colorado Geological Survey. Both sought me out (within the same week!) on finding this site, and both have been extraordinarily generous with their time and knowledge ever since — despite the fact that no good deed goes unpunished when it comes to putting up with my questions. Their perspectives on the history of Colorado geology remind me that with the excitement of any new finding or synthesis must come a healthy dose of caution and a look back to the quality of the original data. 

Kathy, Matt & Casey

Finally, I'm hopelessly indebted to my wife Kathy, son Matt and daughter Casey for putting up with the endless side excursions to points of geologic interest ("It'll just take 30 minutes, honey, I swear."), the incessant photos ("Wait, I can't leave without snagging that gorgeous contact over there. It'll just take 10 minutes, honey, I swear.") and the predictable last-minute book consultations ("I'll catch up with you down the trail as soon as I look up this formation. It'll just take 5 minutes, honey, I swear.") that riddle every family trip. They are more patient than I deserve, and Kathy always graciously accepts more than her fair share of the driving while I feverishly thumb through my briefcase full of geology references en route to the next attraction.

Top    Page Index

General References

Southern Rockies (red square) in context

Listed alphabetically by title below are excellent online and hardcopy resources for anyone interested in the geology behind Colorado's incomparable scenery. This site relies heavily on many of them. The references likely to be most useful are marked with double stars "**". See also the more topical references at the end of each article on this site—particularly those cited in the groundwork articles Colorado Geology Overview and Earth At Work.

• A Guide to the Rimrock Drive, Colorado National Monument, 3rd ed., 2000, by Rose Houk, Colorado National Monument Association

• Annals of the Former World, 1998, by John McPhee, Farrar, Straus and Giroux

• ** Ancient Denvers — Scenes from the Past 300 Million Years of the Colorado Front Range, 2001, by Johnson KR and Raynolds RG of the ^Denver Museum of Nature and Science, now ^online and augmented with many superb new geologic maps and diagrams.

• ** Colorado Geologic Highway Map and Shaded Elevation Map, GTR Mapping with the cooperation of the ^Colorado Geological Survey, 2002 (available at ^MAPSCO, Denver, CO). A must for every glove box. I cut my teeth on the 1991 revision, but this updated geologic map shows Fourteeners for better localization of contacts, and the new shaded elevation is much more useful than the previous unannotated shaded relief map. 

• **^Colorado Geological Survey web site — lots of must-have Colorado geology resources, including several ^field trip guides, an excellent and very revealing downloadable ^Colorado shaded relief map, a ^map of Colorado's major tectonic and geographic features and a ^Colorado earthquake map among many others.

• ** Colorado Recreational Road Atlas, Pierson Guides, 1991 (available at ^MAPSCO, Denver, CO) — detailed coverage of the entire state on a shaded relief background, with most of the best unpaved roads marked.

• ** Colorado Seamless USGS Topographic Maps on CD-ROM, 2000, v. 2.6.4 with TOPO! viewer, ^National Geographic Society

• Colorado's Fourteeners, 2nd ed., 2000, by Gerry Roach, Fulcrum Publishing Co.

• ^Friends of Dinosaur Ridge web site — this non-profit organization has sponsored a decade of earth science education at the  Dinosaur Ridge segment of the Dakota Hogback west of Denver.

• Geology by Lightplane— University of Wisconsin geologist and pilot Louis Maher shares with us his highly illuminating collection of aerial photographs of geologic interest. He also shares high-resolution versions of his photos via FTP. Nothing imparts an appreciation of the geometry and provenance of a major landform as immediately as a well-chosen aerial view.

• Guide Book to the Geology of Red Rocks Park and Vicinity by Andrew M. Taylor, 1992, Cataract Lode Mining Company (available at the Dinosaur Ridge Visitor's Center and at The Tattered Cover bookstore in Denver)

• ** Guide to the Geology of Colorado by Andrew M. Taylor, 1999, Cataract Lode Mining Company (available at the Dinosaur Ridge Visitor's Center, The Tattered Cover bookstore in Denver, and at the Colorado National Monument Visitor's Center)

• Heart of the Desert Wild, Grand Staircase-Escalante National Monument, 2000, by Greer K. Chesher with photographs by Liz Hymans, Bryce Canyon Natural History Association

• ** Hiking Colorado's Geology by Ralph and Lindy Hopkins, 2000, ^The Mountaineers

• James Madison University Geologic Web Sites — Lynn Fitcher's excellent compendium of online geologic tutorials

• ** ^Jules Verne Voyager, Jr. — UNAVCO's impressive interactive online global tectonic viewer and map server.

• ** Messages in Stone: Colorado's Colorful Geology, 2003, Colorado Geological Survey, Matthews V, KellerLynn K, Fox B, eds. — a gorgeously illustrated guide to the state's varied and often world-class geology, with authoritative text by the geologists of the ^Colorado Geological Survey.

• ^PALEOMAP Project — this impressive site by Christopher R. Scotese features still and animated plate tectonic reconstructions dating back to the late Precambrian.

• Plate Tectonics: An Insider's History of the Modern Theory of the Earth, 2001, Naomi Oreskes, ed., Westview Press

• ^Popular Geology — geologist Dick Gibson's witty portal to lay geology articles and online resources 

• ** Roadside Geology of Colorado, 2nd ed., 2002, by Halka Chronic and Felicie Williams, ^Mountain Press — an invaluable start on the identification and understanding of the rocks and structures visible from Colorado's highways, this updated edition covers most of the state with variably detailed text, maps and photographs. Some of the theories and explanations are dated now, but the prose is very accessible, and the book remains a valuable guide worthy of any glovebox. 

• ^Rocky Mountain Association of Geologists web site — Denver-based RMAG serves petroleum and mining geologists primarily, but its excellent ^On the Rocks field trips are open to anyone interested. 

• The Mountain Geologist, v. 38, no. 3, July, 2001 — a special issue of the journal of the ^Rocky Mountain Association of Geologists devoted to Dinosaur Ridge (available at the Dinosaur Ridge Visitor's Center)

• The New Summit Hiker by Mary Ellen Gilliland, 1999, Alpenrose Press

• ** ^This Dynamic Earth: The Story of Plate Tectonics — a well-illustrated USGS educational site by W. Jacqueline Kious and Robert Tilling

• ^Virtual Field Trips — brief descriptions and illustrations of field trips of general interest sponsored by the Rocky Mountain Association of Geologists.

• ** ^Visible Earth — a treasure trove of spectacular public domain NASA photos

• ** ^Web Geological Time Machine— the University of California (Berkeley) Museum of Paleontology publishes this excellent online geologic timescale with hyperlinks to explanations of the boundaries separating the time divisions. 

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