Started by Lockwood, perpetuated by Silver Fox... [UPDATE: Geology Happens, Geotripper, Hypocentre & Phreatic Ramblings have chimed in, too. The latter even posted about a huge paleofalls...] As per the geoblogospheric standard, the idea is to bold the ones you've been to.

#10 Lower Calf Creek Falls, Escalante National Monument, Utah
#9 Lower Falls of the Yellowstone River, Yellowstone National Park, Wyoming
#8 Upper Whitewater Falls, in southwestern North Carolina
#7 Snoqualmie Falls, between Snoqualmie and Fall City, Washington
#6 Havasu Falls, Supai Village, Havasupai Indian Reservation, Grand Canyon, Arizona
#5 Shoshone Falls, Twin Falls, Idaho
#4 Multnomah Falls, Columbia River Gorge, Oregon
#3 Bridalveil Falls, Yosemite National Park, California
#2 McWay Falls in Julia Pfeiffer Burns State Park, Big Sur, California
#1 Niagara Falls, Niagara, New York

Bonus Waterfall #1 [via Lockwood]: Salt Creek Falls, Oregon
Bonus Waterfall #2 [via Silver Fox]: Palouse Falls, eastern Washington
Bonus Waterfall #3 [from me]: Deer Creek Falls, Grand Canyon, Arizona (photo above)

For the record, I kind of don't get the appeal of waterfalls. I mean, they're cool and all, but they don't strike as particularly complex (and therefore, not particularly interesting)... I mean: gravity, right? ...It pulls water downhill... What's the big deal? (I had a conversation this summer along these lines at Waterfall #9 on this list, with a similarly-minded fluvial curmudgeon.)

...But people love them - When I poll my Physical Geology students at the end of the semester about what their favorite part of our Billy Goat Trail geology field trip, only a third or so invoke the migmatite, a third or so cite the physical challenge of climbing "The Traverse," and a third or so claim that viewing Great Falls was their favorite part. To each their own, I reckon: I'm glad they got something meaningful out of the trip... but I can't claim to understand it.

In my twisted worldview, Deer Creek Falls is interesting not merely because it's scenic (and a great place to go swimming), but because the waterfall issues from the Great Unconformity, and thus has geologic significance: It satisfies the intellect as well as aesthetic sensibilities.

Labels: arizona, california, grand canyon, new york, wyoming

The International Year of Planet Earth may have declared a list of "the Earth's ten most spectacular places." At least that's what they're saying at the Discovery Channel's new Discovery Earth site, where they have a rundown of all ten (with photos). (No mention of it at the IYPE site, though: It may be that the Discovery Channel is just highlighting ten of the many, many U.N. World Heritage sites... their language is unclear as to who decided on these particular ten.)

Regardless, the photos will whet your appetite. With my visits in bold, they are:

• The Giant's Causeway, Northern Ireland (posts on NOVA Geoblog)
• Wadi Al-Hitan (Valley of the Whales), Egypt (Eric's been posting on this recently)
• Lake Baikal, Siberia (deep, big)
• Komodo National Park, Indonesia (big monitor lizards; my friend Kenny has been)
• Grand Canyon, Arizona, USA (posts on NOVA Geoblog)
• Ilulissat Icefjord, Denmark (glacial beauty)
• Wulingyuan, China (quartzite pillars and indigenous fauna)
• Surtsey, Iceland (46 years old this year)
• Central Amazon, Brazil
• Great Barrier Reef, Australia

Labels: antrim coast, asia, australia, china, fossils, giants causeway, glaciation, grand canyon, ice, reefs, south america, travel, water resources

When critters interact with their environment, sometimes they leave behind traces of that interaction. If we're lucky, these traces fossilize and can be preserved through time to tell us interesting things about the past. This past summer, when I rafted down the Grand Canyon with my father and two brothers, I saw some cool trace fossils. In chronostratigraphic order (earliest first), here they are:

The Bright Angel Shale can be found atop the Tapeats Sandstone, and below the Muav Limestone along the river in much of the canyon. The Bright Angel is middle Cambrian in age. For my money, it's one of the most spectacular sedimentary layers there, because it's so varied. The colors of the individual strata range from purple to green to brown to tan, and they are in many places chock full of horizontally-oriented feeding traces. Here's some of those wormy shapes along the trail to a waterfall we hiked to... (sorry, don't remember the name or exact location... I think it was day 4 or so of the overall trip... Hmmm, I guess I should have blogged this in early July when I photographed it...)





Nearby, we saw a spectacular trilobite crawling trace (Cruziana?):



Earlier in the trip (day 1, at lunchtime), and higher in the stratigraphic stack (the Permian Coconino Sandstone, which is a sand dune deposit), we saw these reptile (synapsid?) footprints:



This is a trackway left by an ancient reptile as it was walking up and down the dunes, preserved on the slip-face (which defines the feature we recognize from a side-view as "cross bedding"), and now, 260 million years later, I'm viewing those same tracks from underneath, as the older slip-faces of the dune have peeled off, and only the overlying (younger) ones are preserved in this particular alcove. Pretty spectacular stuff. And it offers some nice lunchtime shade, too... Can't complain about that. Here's another shot, with a sense of scale in it:



You can see the individual toes! Wild!

Labels: arizona, cambrian, fossils, grand canyon, permian, primary structures, travel

Another book I read over the winter break was Canyon Solitude, by Patricia C. McCairen. It's a travel book about one woman's solo journey down the Colorado River through the Grand Canyon. It's one of those books that derives its structure from a journey, but it includes plenty of asides, mainly about the author's longer-term personal journey through life. It's rich in a kind of feminine soul-searching which may appeal to female readers, but as a male, I kind of didn't "get" that part. That being said, I'm a fan of travel books, and it was a pleasant enough read. I think it resonated more with me than it would with the average bear because I spent a week on the same journey this summer. Overall, I'd give it 3 stars out of 5 possible.

Here's a link to the book on Amazon.

Labels: arizona, books, grand canyon

Today's science seminar went well. There was a reasonably full house (maybe 150 or 200 people?) and most of them looked reasonably awake all through it. Afterwards, I had some new folks express interest in my Rockies field course for next summer. Additionally, a bunch of the audience stuck around to look at some rock and fossil specimens I had brought along. When I got back to my office, there was a nice note in my in-box from the provost, who had attended and complimented the talk. And then I got a free lunch with three of my colleagues! Chinese food... makes me sleepy, but dang, it was good.

Here's the slideshow I gave, via SlideShare.net (The embedded version below doesn't seem to be working for me, so here's a direct link to the PPT on SlideShare):

Labels: food, fossils, geology, grand canyon, meetings, travel

As a follow-up to yesterday's post on the "Great Unconformity," today I offer a few more shots of unconformities in the Grand Canyon, including (at the end), an angular unconformity...

First, here's a close-up of the contact between the Vishnu Schist and the Tapeats Sandstone:


Slightly blown-out because I was shooting into the sun, and the outcrop was in shadow, but that's why God invented Photoshop:


Same thing, but with the direct light, it's texture (rather than color) that allows you to discern the difference between the two rock units:


The Great Unconformity is visible here, with a boatload of river rafters for scale:


Same thing:


Same thing again...


Okay, here's something different. A waterfall shot. People apparently love waterfalls. Every place I went this summer with a waterfall, there were oodles of folks gathered around, and much flapping of camera shutters. I must be dim, because I kind of don't get it. Water flows downhill... What's the big deal? Anyhow, here the waterfall actually shows us something interesting: note where it emerges from:

That's right -- from the unconformity. Apparently, this is due to the stubborn resistance of the crystalline basement rocks, which are tougher to erode into than the overlying sandstone. The creek cut through the sandstone, but hasn't yet cut through the Vishnu Schist and Zoroaster Granite. However, the Colorado River has, and as the creek flows into the river, there's a difference in the elevation of the two bodies of water. Hence, the waterfall.

I went for a pretty amazing swim in the pool at the base of this fall: the water was cool and bracing, and the wind created by the waterfall was amazingly powerful, actually blowing swimmers downstream! Just the thing after a hot hike.

Lastly, a different aspect of the same unconformity, also seen in the Grand Canyon. Don't look in the foreground, but high up on the distant ridge. This one is an angular unconformity, with sedimentary rocks below the ancient erosional surface as well as above.

In this case, the angular unconformity separates the Grand Canyon Supergroup from the Tapeats. The Tapeats, as we've seen, is Cambrian (~543-488 million years old). The Grand Canyon Supergroup (1.25 billion to 825 million years old) was laid down on the basement rocks first, then faulted and tilted 15 degrees. These tilted blocks were then eroded. On many, the Grand Canyon Supergroup was totally burnished away, re-revealing the underlying basement rocks. In the more down-dropped blocks, however, little protected packages of the Supergroup were preserved. When sea level rose anew in the Cambrian, it deposited the Tapeats Sandstone. In some places, the Tapeats sand was laid down on granite and schist, and in other places on these tilted layers of the Grand Canyon Supergroup. Same erosional surface; different rocks below it in different locations.

Here's a Flash animation showing the various steps it took to put the Grand Canyon together, including the erosion that gave rise to these various unconformities.

Labels: cambrian, grand canyon, primary structures, proterozoic, sediment

This summer, I saw "the Great Unconformity" in a couple of locations.

An unconformity is a break in the local geologic record -- a period of time which elapsed without being recorded by the deposition of rock units. Often unconformities mark places where erosion has erased part of the local rock record, but sometimes they just mark periods of non-deposition. (Analogy: You can get a blank page in your diary two ways. You can either take a day off from writing, or you can write that day's entry and then later go back and erase it. Either way, you end up with a day going by and no journal entry.) People call the major break between metamorphic and igneous "basement" rocks and overlying sedimentary layers the "Great" Unconformity, though it's not the same age everywhere. It's just shorthand, really.

Anyhow, here it is in the Grand Canyon (photos provided below are both unadorned and annotated versions):





Give or take, there's about 1.2 billion years missing along this ancient erosional surface. Intuitively, this probably makes sense, since metamorphic rocks like schist and 'distilled' intrusive rocks like granite are characteristics of mountain belts, where they form at depth. In order to get those interior-mountain-belt rocks to the surface takes lots of erosion over lots of time (though not necessarily that long -- in DC, for instance, we have interior-mountain-belt rocks exposed that 'only' took 360 million years to make it to the surface). In the above photos, the metamorphic rocks and granites below the unconformity formed about 1.7 billion years ago, during the Mazatzal Orogeny, and the sedimentary layers on top (both quartz sandstones) were deposited in the Cambrian period, about 543-488 million years ago. They represent passive margin sedimentation along an ancient transgressive seashore, something like modern day beach sands along the east coast of North America. So, to get something like the Great Unconformity, take something like coastal Maine (Acadia National Park, say), and bury it beneath something like Virginia Beach.

And here "it" is again, in Wyoming's Wind River Canyon (between Thermopolis and Shoshoni):





A zoomed-in look at this same outcrop:





This time, however, the rocks below the unconformity are much older* metamorphics (schist & amphibolite) and granite. According to Maughan (1987), these are the oldest rocks exposed in Wyoming, having formed about 2.9 billion years ago. They were then metamorphosed at 2.75 billion years ago. These truely ancient rocks (Archean) were then eroded and exposed at the surface, where quartz-rich sand was laid down atop their burnished roots. Aside from the difference in the age of the underlying basement rocks, the story is very similar to the one at the Grand Canyon.

* Thanks very much to Kim, who pointed out my error in under-stating their age in an earlier, more-poorly-researched version of this post.

Reference:
Maughan, E.K. (1987) "Wind River Canyon, Wyoming." In: Geological Society of America Centennial Field Guide - Rocky Mountain Section. S.S. Buess, ed. p. 191196.

Labels: archean, cambrian, dc, grand canyon, primary structures, proterozoic, unconformities, wyoming

Sorry for the long delay in posting here. Turns out they don't have Wi-Fi at Phantom Ranch.

After my time in Zion (did Angels Landing and a few other small hikes while there), I scooted down to Las Vegas, Nevada, to pick up my father and two brothers. They had flown in there, and after one day were already tired of the city. I was ready to leave five minutes after I got there, which is always how I feel about Vegas. Somehow, circumstances keep conspiring to bring me back there, though...

We drove out of the Basin & Range and up onto the Colorado Plateau, and spent the night at Cliff Dwellers, a lodge near Marble Canyon. I was really impressed with their food and drink. We had an amazing meal, washed down with several pitchers of Newcastle Brown Ale! In the morning, we gathered up our gear and put onto the river. Our trip consisted of two rafts outfitted with side tubes and motors and guides. One raft was entirely made up of a family from Charlotte, North Carolina, including the glass artist Wayland Cato, III. The Bentley's raft was augmented by a family from Littleton, Colorado, two oil men from Oklahoma, and a couple of veteran river rafters from northern California. It was a motley crew, but we started having fun immediately.

We launched at Lees Ferry, in the Kaibab Limestone, and then descended in both elevation and geologic time. At our first lunch stop, in the Coconino Formation, I was astonished at several synapsid reptile trackways protruding from the underside of the paleo-dune slipfaces overhead. I took some photos, but because of the aforementioned software issue, I won't be able to share them until I get back to DC in August. As the first couple of days went by, we just went deeper and deeper into the Paleozoic stratigraphy of the Colorado Plateau. Of all the formations, my favorite was the Bright Angel Shale, which has many beautiful colors in thin layers throughout (not to mention oodles of trace fossils). I was particularly pleased to play frisbee in a "cave" in the Redwall Limestone, a place that I have shown photographs of to my students, but never actually seen before. It's a HUGE cliff of the Redwall, and then this seemingly small cave etched into its base (and filled with sand), but the cave could easily swallow my building at NOVA: it's big!

At some point, we crossed a major fault, and were instantly dropped down about a billion years in geologic time. Once we got into the Grand Canyon Supergroup and the metamorphic and igneous basement rocks, my geologic interest really went wah-wah. The Vishnu Schist and Zoroaster Granite make a stunning contrast: really beautiful pink cutting across dark grey. I introduced my raft-mates to the idea of the Mazatzal Orogeny, and we discussed how boudinage forms. There were faults and folds galore: structural paradise. I loved it.

Did I mention the rapids? There were rapids. The water was COLD, thanks to Glen Canyon Dam(n). But the sun was hot, and we dried out quickly. Meals were gourmet, though the campsites were spartan (you had to poop in a box that got packed onto the raft each morning: leave no trace!). We slept out under the stars every night, sometimes dealing with blowing sand.

We took several hikes up side canyons to see waterfalls and go swimming. Several of these were good and physically challenging, which is what I wanted. I enjoyed swimming and playing "three-dimensional frisbee" in Havasu Creek, and doing cannonball jumps in the weird blue of the Little Colorado River.

The final day on the river, we came to the western section of the Canyon where recent lava flows (basalt) have cascaded over the rim and down into the canyon. This is famous for producing one of the toughest rapids in the whole Grand Canyon: Lava Falls. But it was awesome to float by and see umpteen gazillion columnar joints, and whole feeder canyons plugged up by basalt. Pretty cool!

Our final morning, we were helicoptered out of the Canyon to a ranch on the rim. This was my first time in a helicopter, and it was giddy and amazing. I want to fly! From the ranch, we transferred to small fixed-wing planes, and I said goodbye to my family. They went back to Vegas, and I flew back to Cliff Dwellers, where my Prius (and a shower!) awaited.

Labels: fossils, geology, grand canyon, minerals, primary structures, rivers, sediment, travel, volcano

I left Bozeman on Saturday morning, and drove for about seven hours. I headed south through Ennis, Montana, along the western side of the Madison Range, passing by the Madison Earthquake Site landslide (from the 1959 Hebgen Lake earthquake), and then south into Idaho. I went through Island Park, Idaho, site of the caldera of one of the three big recent eruptions of the Yellowstone volcanic center. Then into northern Utah, where I got a glimpse of the Great Salt Lake. I headed up into the Wasatch Range to spend the night, just east (and several thousand feet above) Ogden, Utah. I did some birding on the reservoir there, observing the mating rituals of both the woodcock (amazing humming noise produced during flying dives) and the western grebe (neck bobbing following by synchrnonous running across the water).

The next morning, I headed west from there, into the basin, across a range, into another basin, across another range -- you get the idea. I initially intended to go hunt for trilobite fossils in the Wheeler Shale in the House Range, but the 20-mile dirt road rattled me (quite literally) and I turned around after only four miles. I got spooked: what would happen to me if the Prius broke down out here? It's really quite desolate country. I've only ever had that feeling once before, when my Dad and I drove across the Namib Desert. It's a mix of agoraphobia and anxiety over feeling inept at repairing mechanical things, like Prii and other automobiles. I chickened out -- no trilobites for me. But there was a consolation in Great Basin National Park, which was where I headed that afternoon. I did a short hike there in the Snake Range, and toured Lehman Caverns there (my third guided cave tour in two weeks!). I had my best campsite of the trip at Great Basin: montane forest, with a gurgling stream running fifteen feet from my tent. Lovely.

When I woke up, I packed up the car and coasted downhill for eight miles into the town of Baker, Nevada, where I had a great breakfast and coffee at a little cafe there. Then up and over the Snake Range, and down the next valley to the west, south for 93 miles of some of the most empty country I've ever seen in America. In an hour and a half of driving, I saw only 20 vehicles. I crossed back into Utah, and then made my way south to the edge of the Colorado Plateau, and drove up into Zion National Park. Zion is a great canyon cut into a series of sedimentary rocks. The last time I was here, 13 years ago, I walked up the Narrows, and my first order of business was to repeat that hike. There's a new shuttle system in the park now, so after parking at my campsite, I hopped on a shuttle into the park and rode it to the end. I waded into the Virgin River and shuffled upstream. In the Narrows, the Virgin River has cut down through the Navajo Sandstone, but not quite down into the weaker underlying Kayenta Formation, and so the canyon is deep but narrow. (Downstream, when it gets deep enough to tap into the Kayenta, it undermines the sandstone cliffs, and the valley widens.) "Hiking" here is one of the more unique outdoor experiences I've had. Being immersed in the cool river, surrounded by towering rock walls -- it's magical. The further upriver you hike, the less people there are, and it's like a cathedral. I went up and around several entrenched meanders, and marvelled at the alcoves, cross-bedding, and variety of cobbles in the riverbed.

Today, I'm staying in the park and heading up to Angel's Landing, a legendary hike in its own right. Tomorrow morning, bright and early, I'm off to Las Vegas to pick up my Dad and brothers for our Grand Canyon rafting trip. Not sure if I'll be able to post again until after I get out.... late next week.

Labels: birdies, fossils, grand canyon, idaho, montana, national parks, stratigraphy, travel, utah

It's been a busy week for me. I've really enjoyed my first MSSE class of the summer, Dave Lageson's "Northern Rocky Mountain Geology." Dave led us on a series of field trips within driving distance of Bozeman: the Bridger Range, the Paradise Valley, the Spanish Peaks, the Hebgen Lake earthquake scarp and Quake Lake, and today out to Ringing Rocks, the Lahood Conglomerate, and a descent into Lewis and Clark Caverns. It's been a lot of cool geology, as well as a lot of driving! In the evenings, I've been keeping busy with Shakespeare in the Parks, seeing the B Side Players, and socializing with fellow MSSE teachers. All good stuff, but it leaves little time for blogging. Tomorrow morning, I'm off to the south. I'll be on the road for another five days or so, going to Las Vegas to pick up my father and brothers and then we're going rafting down the Grand Canyon starting next Wednesday. Along the way, I hope to visit some sites in Utah, and I hope to post some updates en route. After the Canyon float, I'll head back north, again through Utah and probably western Colorado (Black Canyon of the Gunnison), before returning to Bozeman for another three MSSE classes ("Dinosaur Paleontology of the Hell Creek Formation," "Life in Extreme Environments," and "Wildlife Ecology of the Greater Yellowstone Ecosystem"). Then back east, hopefully with some Niobrara Chalk and Pierre Shale site visits along the way.

Also, along similar "rock and road" lines, I had an article published in Geotimes this month on the roadtrip I did two years ago from DC up to Alaska and back. You can check it out here.

FYI, I got a new camera for this trip, and haven't been able to download any pictures off it yet (a stupid software issue), so that's the reason for the lack of photos lately. My apologies!

Labels: grand canyon, montana, msse, utah

The talented science writer Joel Achenbach has a piece on the Washington Post website about new research which suggests the Grand Canyon as an erosional feature is much older (~17 Ma) than we previously thought (~6 Ma). Achenbach's article is based on a study published in today's Science by Victor Polyak, Carol Hill, and Yemane Asmerom, of the University of New Mexico. These researchers* calculated the ages of cave mammillaries (rounded speleothems that form in caves near the water table) with U/Pb isotopic dating to infer when the water table had dropped in the past, implying a deep canyon.

* With all the talk in the geoblogosphere about death-defying geological research, it should be noted these folks were rappelling hundreds of feet down the canyon's cliffs to get to some of these caves...

Anyhow, dates from the calcite deposits suggest that the water table dropped more slowly (and hence the erosion rate must have been slower) in the western canyon than in the eastern section. The western part of the canyon yields inferred erosion rates of 55 to 123 m/Ma, while the eastern canyon's caves yield inferred rates of 166 to 411 m/Ma (about 3 times as fast). The authors interpret this to mean the Grand Canyon formed in two pieces: one started slowly propagating from the west, then another formed from the east (relatively rapidly working its way westward), and the two broke through and met in the middle, yielding the Canyon we know and love.

The photo above is a view from one of the sampled caves. [Photo is by Art Palmer, taken from the "Achenblog" site (Joel Achenbach's blog).]

Check out more details here. Or see the NYT's treatment here.

Main reference:
Victor Polyak, Carol Hill, and Yemane Asmerom, 7 March 2008. "Age and Evolution of the Grand Canyon Revealed by U-Pb Dating of Water Table-Type Speleothems." Science, Vol. 319. no. 5868, p. 1377 - 1380. DOI: 10.1126/science.1151248

Commentary in the same issue of Science:
Tim Atkinson and Mike Leeder. 7 March 2008. "Canyon Cutting on a Grand Time Scale." Science, Vol. 319, no. 5868, p.1343-1344. DOI: 10.1126/science.1155286

Labels: caves, grand canyon

A new paper in Water Resources Research suggests that Lake Mead, Nevada, may be dry by the year 2021. Authors Tim Barnett and David Pierce (both of Scripps) base this austere prediction on two things: (1) increasing projected rates of water use in the American southwest, as well as (2) climate change projections which suggest the region will receive less precipitation. They also posit a 50% chance that the lake level will drop too low to allow hydroelectric power generation by 2017. That's only 9 years from now!

It would seem that it's time for some conservation measures. When I lived out in California, I was struck by a major design flaw in the aqueducts which transport water from reservoirs in the Sierras and the Colorado River system to the centers of population: they're uncovered! These big long uncovered troughs full of water encourage the active evaporation of much of the liquid they carry. I'd imagine that just putting some tarps over the top of them would make a huge difference in conserving water that would otherwise be lost to the atmosphere. Maybe this has already happened: I left California in 1998, and I recall some post-September-11 (2001) talk about how the aqueducts were susceptible to being poisoned, so maybe they've already been covered up in the name of homeland security.

Check out the picture of the lake in October of last year (by Ken Dewey of the University of Nebraska). A glaring white "bathtub ring" shows how much the lake level has dropped due to the recent string of drought years the west has experienced. In early July, at the end of our Grand Canyon rafting trip, my Dad and brothers and I will float into the upper reaches of Lake Mead, and we'll likely see something like this in person. I'll be sure to post a blog reaction to that when I see it.

Reference:

Barnett, T. P., and D. W. Pierce (2008), "When Will Lake Mead go Dry?," Water Resour. Res., doi:10.1029/2007WR006704, in press.

For more details on the new study, see the press release on Eurekalert.

Labels: global warming, grand canyon, water resources

You may have seen Ron Blakely's excellent paleogeographic maps of the North American continent. Browsing around his site the other day, I found this nice sequential cartoon of the geologic steps it took to build up the rocks at the Grand Canyon.

My dad and my two brothers and I are going rafting down the Canyon this summer, and I'm looking forward to exploring the geology firsthand from the river level. My four previous trips to the Canyon have all started at the rim, then hiked down (sometimes to Plateau Point, sometimes to the river), and then back up in the same day. Staying at river level for over a week ought to be awesome.

Labels: art, geology, grand canyon

In preparation for this summer's rafting trip down the Grand Canyon with my father & two brothers, I checked out the book An Introduction to Grand Canyon Geology from the NOVA library. The author is L. Greer Price. It's a slim little book, in full color, with lots of little boxes inserted amid the main text. These boxes explore smaller subtopics like stromatolites or rock color. The main text emphasizes the chronological sequence of steps to create the bedrock of the Canyon, and then a detailed discussion of how rock structure and erosional effects combine to carve the land into a shape as varied as the Grand Canyon. It's a book a lot like the one I'm working on for the C&O Canal.

I've visited the Grand Canyon four times, so I've managed to get a lot of the upper stratigraphy down. I picked up this book to bulk up my understanding of the deeper gorge (where my family & I will be spending our time in June). While a lot of the book was geological boiler-plate about plate tectonics and superposition, I learned some new details. For instance, I had no idea the Cenozoic was represented at all in the Canyon, but apparently the remains ("still pungent") of a Shasta Ground Sloth were discovered in Rampart Cave (a cave in the Muav Limestone) in the western Canyon.

The writing style is balanced. I could see how the author struggled with being technically accurate but also accessible to the wide audience he was writing for: the Mazatzal Orogeny (~1.7 Ga) is described, but it's not called the "Mazatzal Orogeny." Another example would be in describing Mesozoic subduction on the west coast, Greer swaps out the technically-correct name Farallon plate for the more recognizable "Pacific" plate, even if that's not technically correct.

The book is short (59 pages), and it's 50% pictures -- an easy read in an afternoon.

Labels: books, grand canyon