The Abandoned Lands...A Journey Through the Colorado Plateau: 700 years in the Fertile Cresent

It's been a bit of time since we checked in on our journey through the Abandoned Lands, my theme for our summer field studies in the geology and archaeology of the Colorado Plateau. In the previous post of the series we were looking into the abandonment of Chaco Canyon after 300 years of cultural dominance. The reasons may have been meteorological and geological: the land was worn out and droughts had intensified by 1150 AD. On this day, we had traveled a hundred miles north to Durango, and over a series of foothills of the San Juan Mountains to arrive at Mesa Verde National Park. It was our first look at the 'fertile crescent' of the Ancestral Pueblo people. And a place that held out more than a century after the influence of Chaco Canyon had faded away.

World history taught us about a different fertile crescent, the one that spawned human civilization in the Middle East. In the case of the Colorado Plateau, it was a landscape that supported humans for 700 years or more, before being abandoned in the late 1200s. The land lying between Mesa Verde on the east and Cedar Mesa to the west was the sweet spot for agricultural development: it was a critical thousand or feet higher than the hot dry desert around Chaco Canyon, but it was not so high as to be buried by snow for too much of the year. The lands between Cortez, Colorado and Blanding, Utah were covered by the Dakota Sandstone and an overlying weathering unit called the Dove Creek Soil. It was ideal for growing corn and beans centuries ago, and continues to produce pinto beans today.

We are in one of our nation's premier national parks, famous for the spectacular cliff dwellings, but today's post doesn't have any pictures of them. Instead, I am showcasing the land on which the Ancestral Pueblo people lived. And what could be more boring, really? The plateau of the "Green Mesa" is mostly a gently-sloping pinyon-juniper woodland that has been scarred by a series of disastrous wildfires in the last few years. In a bizarre kind of way, it reminded me of home, back in the Central Valley of California. But this barren burned landscape probably looks more like the ancestral landscape of the Pueblo people right now than it has in hundreds of years. Why? Because this barren surface was their farmland, cleared of trees and shrubs in favor of corn and beans. For 600 of their 700 years on this mesa, it was the location of their village sites as well. The famous cliff dwellings of Mesa Verde were occupied for barely a century!

Mesa Verde has something like 5,000 archaeological sites, and yet only a dozen or so cliff dwellings are the objective of the majority of visitors. The older mesa-top structures garner a great deal less attention by visitors in a hurry, but they are a fascinating record of an occupation that lasted three times as long as the United States has existed. The pit houses, small villages, and the Sun Temple are interesting and more intimate places to visit than many of the cliff houses which often can only be seen from across canyons. There is even a reservoir and terraces that were constructed to expand arable farmlands.

The canyons are for the most part dangerously inaccessible, and I imagine they were utilized mostly as a source of water. Until that last century, that is. Then the inaccessible alcoves became home. Which leaves us with the big questions: why did the Ancestral Pueblo move into these dangerous canyons, and why did they abandon this land only a century later?

A programming note: Our exploration of Mesa Verde had one little quirk that I don't think has ever happened in all my journeys in the digital age...I left my camera sitting in my tent back at camp! These pictures were kindly provided by Mrs. Geotripper.

Death Valley Retroactively Claims Title for Hottest Place on the Planet

The concept of "retroactive retirement" became an amusing issue in the presidential campaign as a way of a particular politician escaping from an unpopular position by more or less going back in time to say he had retired when it looked like he hadn't (see the New Yorker response here). I came across an interesting abstract that outlines how meteorological researchers have retroactively declared Death Valley National Park as the hottest place in the world, based on an observation in 1913 when the temperature reached 56.7 degrees Celsius (134 degrees Fahrenheit). The story was picked up by NBC news where I first came across the information.

The gist of the argument is that the meteorologists have doubts about the circumstances of the measurement in Libya: an obsolete thermometer, inexperienced observer and improper positioning of the apparatus (apparently over asphalt). Nearby areas did not record corresponding record temperatures. So the record reverts to the 1913 reading at Death Valley.

It's an interesting convergence of records, because Death Valley made the news this year for another meteorological world record: the highest overnight temperature ever recorded on Earth. On July 12 of this year the low temperature at Death Valley, California dropped to only 107°F (41.7°C).  Because the daytime high was128° (53.3°C), the average temperature of 117.5°F made that day the warmest 24-hour temperature on record. Ever.

And that, my friends, is why I visit Death Valley in February.

PS: Jeff Master was on this story first today

Just Published! Geological Excursions in the Sonora Pass Region of the Sierra Nevada (and cute furry animal)

The newest guide by the Far Western Section of the National Association of Geoscience Teachers is now available for sale! Geological Excursions in the Sonora Pass Region of the Sierra Nevada, edited by Noah Hughes and yours truly, is a series of field trips at Sonora Pass and along the eastern Sierra Nevada as far south as June Lake and Saddlebag Lake near Tioga Pass. Other excursions include significant geologic sites on the Stanislaus River, including the unique Natural Bridges near the town of Columbia.

This is a fascinating region that hasn't always received the attention it deserves. A great deal of recent research has been done on the Miocene volcanism in the region and how it relates to the uplift history of the Sierra Nevada and the development of the Sierra Nevada microplate. The region is part of the Walker Lane, which in all likelihood is the future margin of the North American Plate. There are ghost towns, saline lakes, ancient metamorphic rocks glacial deposits and a strange "fluvial forest" in the West Walker River. There is the strange "Reversed Creek" near June Lake.

Chapters in the book include the following:

A Geographical Sketch of the Central Sierra Nevada

A Brief Overview of the Basement Rocks of the Central Sierra Nevada

Trip 1: Sierra Crest Graben: A Miocene Walker Lane Pull-Apart in the Ancestral
Cascades Arc at Sonora Pass (by Cathy Busby, Alice Koerner, Jeanette Hagan, and Graham Andrews at the University of California, Santa Barbara)

Trip 2: A Guide to the Geology of the Eastern Sierra Nevada between Sonora Pass
and June Lake, California (by Garry Hayes, Modesto Junior College)

Trip 3: Geology and Climatology of the Saddlebag Lake Region near
Tioga Pass, CA (by Ryan Hollister of Turlock High School and Laura Hollister of Pitman High School)

Trip 4: Sword Lake Debris Flow (by Jeff Tolhurst, Columbia College)

Trip 5: Unique Geology along the Stanislaus River, Western Central Sierra Nevada (by Noah Hughes, Modesto Junior College)

Appendix A: The Flora of Central California: Central Valley to the Great Basin (by Mary Cook, Modesto Junior College)

The book was prepared for the Fall 2012 meeting of the Far Western Section of the National Association of Geoscience Teachers held last weekend at the High Sierra Institute at Baker Station below Sonora Pass. All proceeds from the sale of the book support scholarships for geology majors in California, Nevada and Hawaii (details of the scholarship can be found here).

At this time, the book can be ordered directly from the Far Western Section at http://nagt-fws.org/publications.html for $29.95 plus shipping and handling (checks only). The web page also includes dozens of other guides for geological tours all over California and Nevada. The guide will soon be available from Sunbelt Publishing, which published the volume (http://www.sunbeltbook.com/). The ISBN number is 978-0-9606704-4-4.

Photo by Ryan Hollister

We are excited to be able to offer this exploration of a fascinating region! If you are interested in seeing some unique landscapes and want to catch up with some new Sierra Nevada research, check it out (and help some worthy students advance their studies in geology at the same time).

Photo by Ryan Hollister

Here is the promised furry animal. The pika is a rodent adapted to living at the highest elevations in the Sierra Nevada. Their habitat is being affected by global warming. They can be seen near Sonora Pass and in the region above Saddlebag Lake.

The Abandoned Lands...A Journey Through the Colorado Plateau: The Rise and Fall of Empires, Part 3

An empire ended...

We've been following a route through the Colorado Plateau through what I've been calling the Abandoned Lands. It is a journey through some spectacular geology, but it is a journey that reveals some illuminating anthropology as well. We started at the end of a long journey of a people as they found homes along the Rio Grande River and its tributaries (Acoma and Taos), and then explored the dwellings that formed the midpoint of their migration ( Bandelier National Monument). In the last post of the series we had reached their starting point, at Chaco Canyon in northwest New Mexico.

For three hundred years, Chaco Canyon was the spiritual and economic center of the Ancestral Pueblo Universe. And then it was abandoned. Not with an ultimate battle against more powerful invaders, but with a whimper, a decline that took a number of years. Buildings weren't burned down (for the most part), but were cleaned out and sometimes sealed. It was an abandonment driven by the inability of the land to provide enough in the way of basic needs: water, crops and lumber. 

There was little timber in the region to start with, but they used vast amounts of conifer trees that had been hauled fifty miles or more. As the pueblos grew and the need for wood increased, the Ancestral Puebloans constructed roads to facilitate the importation from distant forests.

Casa Rinconada with Cliff House Sandstone and slopes of Menefee Formation.

The region probably never allowed for much in the way of agricultural production. In the desert climate, crops were always a marginal proposition. The people of Chaco imported maize from far-flung locations over distances of twenty or thirty miles.

An unexcavated ruin at Pueblo del Arroyo partially exposed by gullying.

Water was  also a challenge. There were no permanent rivers, and few springs. The problem was made worse by poor treatment of the soils which led to gully development that lowered the area's water table. Crops could be imported and so could wood. Water was another matter.

An unexcavated ruin near Pueblo del Arroyo, with Cliff House Sandstone in the distance.

A fifty year drought began around 1130 AD. It was the beginning of the end. Some of the outlying villages were abandoned first, and as the drought deepened, the main Great Houses were left behind as well. The area became the domain of ghosts and lost spirits (if your imagination is imaginative enough to hear their whispers).

What can we learn? Probably not that much. I mostly think about metropolitan centers like Las Vegas and Phoenix which are totally dependent on the importation of water over distances of hundreds of miles. They depend on energy and food imports from hundreds or even thousands of miles away. We can say that modern technology will continue to support the resource needs of millions of people, but what happens when the petroleum stocks start to run low (despite high prices, worldwide production of oil has remained flat for 6-7 years). And we are in the midst of a disturbing drought that climate scientists think will be the norm for decades to come. Are we thinking about the kinds of choices that must be made?

In the last post we explored Pueblo Bonito, one of the most completely excavated ruins at Chaco. The pictures today are from Pueblo del Arroyo and Casa Rinconada, which have large sections still buried beneath the sand. Modern archaeology recognizes that methods of analysis will improve in future years, and as such we need to leave some of the sites undisturbed. It also provides to visitors like myself a sense of mystery. What still lies hidden???

Three kivas built over the centuries on top of each other.

An empire ended...

Accretionary Wedge #49: It's just out of this world! Hollywood and the Cosmos

It's time for an Accretionary Wedge! Specifically Wedge #49, hosted by Dana at En Tequila es Verdad. The topic is essentially anything exogeologic, that is, beyond the confines of planet Earth. I'm taking the broadly interpreted topic and turning my contribution into a quiz.

Lots of Hollywood movies take place in space and on other planets, and since the director can't go to the other planets, locales on Earth have to suffice. As geologists know, there are landscapes on our planet that do a good job of looking otherworldly, and so geology became a central part of the movie plot.

Sooo....how well do you know your planet, and how well do you know sci-fi movies? Name as many localities as you can in the pictures below, and name the movies in which these landscapes starred.

1) Sand dunes and dark ridges in the distance....

2) A very deep valley in a dry place....

3) Very strange knobs of sandstone...

4) And more sandstone. All the action took place among the red rocks in the foreground. A famous captain bought it here....

5) A glacial lake and alpine peaks...

Picture by Doug Dolde (http://en.wikipedia.org/wiki/File:Ghosts_of_Trona.jpg)

and 6) Some strange towers of calcium carbonate...

And what places did I forget? What would you add to a quiz like this?

Siccar Point, One of the Most Important Field Sites in Historical Geology is Threatened...with Agricultural Sewage

Siccar Point is in the far distance on the left

The abyss of time is about to become a cesspool...

An issue has crossed my desk that ought to be upsetting to anyone who has followed geology as a career or has any passing interest in the history of geology. Siccar Point in southern Scotland is under serious threat of "development". Not development as in hotels and parking lots, but as in "being turned into a pile of sewage". An agricultural company is proposing to cut a pipeline through the point, to be used to transport rotting vegetables and agricultural wastes, untreated, into the sea a very short distance offshore. Information about this desecration and efforts being made to stop it can be found here: http://www.savesiccarpoint.co.uk/. The response time is very short, so I hope that as many geologists as possible will be heard from.

Geotripper lends scale to an outcrop of the crossbedded Old Red Sandstone

I had a single chance to visit Siccar Point back in 2001. We made all the special arrangements with the touring company to get to the locality on the back roads, but a rather awful incident in Scotland interfered in a big way: hoof and mouth disease. The malady was detected and wholesale destruction of the cattle herds in the country followed. The few unaffected herds were placed in quarantine, and no one was allowed to cross pastures (which was necessary to get to the point). One cannot imagine how disappointed we were. I started studying the maps and realized that a second access point might exist, one that wouldn't threaten any herd animals. We drove to a campground at Pease Bay and started walking along the shoreline (actually, I was running, an act that is legend in our department; it was pretty rugged and I should have broken something). We were able to get within sight of the point (it's the point of rocks in the farthest distance of the top picture; click on the picture for a better view).

Although we couldn't stand on the Siccar Point unconformity, a lesser exposure was visible along the shoreline cliffs.

Why is the point important in the history of geology? There is an angular unconformity between the Old Red Sandstone and the underlying graywacke sandstones that provided the most vivid evidence of James Hutton's revolutionary idea of uniformitarianism, the principle that was the impetus for the modern development of geology as a science. John Playfair's description of his visit to Siccar Point is one of the more stirring descriptions of deep time as you will ever read:

"The ridge of the Lammermuir Hills in the south of Scotland, consists of

primary micaceous schistus, and extends from St. Abb's head westward, till it

joins the metalliferous mountains above the source of the Clyde. The

sea-coast affords a transverse section of this alpine tract at its eastern

extremity, and exhibits the change from the primary to the secondary strata,

both on the south and on the north. Dr. Hutton wished particularly to examine

the latter of these, and on this occasion Sir James Hall and I had the

pleasure to accompany him. We sailed in a boat from Dunglass, on a day when

the fineness of the weather permitted us to keep close to the foot of the

rocks which line the shore in that quarter, directing our course southwards,

in search of the termination of the secondary strata. We made a high rocky

point or headland, the Siccar, near which, from our observations on the

shore, we knew that the object we were in search of was likely to be

discovered. On landing at this point, we found that we actually trod on the

primeval rock, which forms alternately the base and the summit of the present

land. It is here a micaceous schistus, in beds nearly vertical, highly

indurated, and stretching from south-east to north-west. The surface of this

rock runs with a moderate ascent from the level of low-water, at which we

landed, nearly to that of high-water, where the schistus has a thin covering

of red horizontal sandstone laid over it; and this sandstone, at the distance

of a few yards farther back, rises into a very high perpendicular cliff.

Here, therefore, the immediate contact of the two rocks is not only visible,

but is curiously dissected and laid open by the action of waves. The rugged

tops of the schistus are seen penetrating into the horizontal beds of

sandstone, and the lowest of these last form a breccia containing fragments

of schistus, some round and others angular, united by an arenaceous cement.

Dr. Hutton was highly pleased with appearances that set in so clear a light

the different formations of the parts which compose the exterior crust of the

earth, and where all the circumstances were combined that could render the

observation satisfactory and precise. On us who saw these phenomena for the

first time, the impression made will not easily be forgotten. The palpable

evidence presented to us, of one of the most extraordinary and important

facts in the natural history of the earth, gave a reality and substance to

those theoretical speculations, which, however probable, had never till now

been directly authenticated by the testimony of the senses. We often said to

ourselves, What clearer evidence could we have had of the different formation

of these rocks, and of the long interval which separated their formation, had

we actually seen them emerging from the bosom the deep? We felt ourselves

necessarily carried back to the time when the schistus on which we stood was

yet at the bottom of the sea, and when the sandstone before us was only

beginning to be deposited in the shape of sand or mud, from the waters of a

superincumbent ocean. An epocha still more remote presented itself, when even

the most ancient of these rocks instead of standing upright in vertical beds,

lay in horizontal planes at the bottom of the sea, and was not yet disturbed

by that immeasurable force which has burst asunder the solid pavement of the

globe. Revolutions still more remote appeared in the distance of this

extraordinary perspective. The mind seemed to grow giddy by looking so far

into the abyss of time; and while we listened with earnestness and admiration

to the philosopher who was now unfolding to us the order and series of these

wonderful events, we became sensible how much farther reason may sometimes go

than imagination can venture to follow. As for the rest, we were truly

fortunate in the course we had pursued in this excursion; a great number of

other curious and important facts presented themselves, and we returned,

having collected, in one day, more ample materials for future speculation,

than have sometimes resulted from years of diligent and laborious research."

A nice exposure of the Old Red Sandstone near Pease Bay.

Standing at (or near, in my case) Siccar Point should be near the top of any geologist's life list. To mar it with a pipeline and sewage...you might as well build sewage treatment plant in the middle of Stonehenge. This shouldn't be happening. All geologists should be heard from as soon as possible to stop this wanton destruction of one of the most important outcrops in the world. It should be under protection as a World Heritage Site, but instead is subject to abuse and misuse. Please make yourself heard, and soon.

Why Did the Military Get Such Nice Digs? Fort Baker on San Francisco Bay

The reasons are partly geological. But before we mention the geology, there must be pictures of cute and interesting animals...like this young sea lion that was eying the crowd of fisherman on the wharf. We were in the Bay Area today celebrating a birthday, but everywhere we went was crowded, as if it were a holiday weekend or something. No parking on the beach at Half Moon Bay. Nothing at either end of the Golden Gate Bridge. The Marin Headlands didn't look particularly crowded from a distance, but the offramp on 101 was backed up for a quarter mile. There was a crowded art festival at Sausalito. We despaired of finding any place to hang out, but a short distance from Sausalito we found a quiet uncrowded park that had somehow missed my notice in the past: Fort Baker.

The military got all the best spots on San Francisco Bay. The Presidio is a huge complex on the northernmost part of the San Francisco peninsula, and the Marin Headlands were covered with forts and outposts, as well as an imposing group of gun batteries. It isn't hard to figure out why. Before the days when wars could be fought with buttons and missiles and drones, you had to assault other countries with some kind of invading force, and if the countries were bounded by shorelines, you had to invade with ships. A brief look at a map of the California coastline reveals that the state has a grand total of two natural harbors: San Francisco Bay, and Coronado Bay down south at San Diego. Two harbors that controlled essentially all major ship traffic south of the Columbia River in Oregon and Washington. Strategically, this is a vulnerability.

The eastern and southern coasts of the United States are geologically stable and are replete with fine harbors as a result of the steep rise in sea level that accompanied the melting of the glaciers at the end of the last Ice Age. River mouths were drowned, providing extensive bays, and deep anchorages.

California is different. It sits on an active plate boundary, the San Andreas transform, and many parts of the coast rise steeply from the depths of the sea. The tectonic uplift has been geologically rapid, and erosion has not kept up in most places. The one exception in central California is San Francisco where the Sacramento/San Joaquin river system was able to carve a canyon through the rapidly rising Coast Ranges. When the ice ages ended, the rise of sea level filled the lower canyon of the Sacramento and San Francisco Bay was the result.

Fort Baker dates from around 1905 when the United States military was beginning to realize the vulnerability of the west coast to attacks by sea. By the time World War II rolled around, the hills above the Golden Gate bristled with cannons. Any armada that tried to enter San Francisco Bay would have been carved to pieces by the crossfire.

The nature of warfare has changed and the gun emplacements and military forts at San Francisco became obsolete. The Presidio was given over to the National Park Service in 1994, and the last soldiers left Fort Baker in 2000. The areas are now managed as part of the Golden Gate National Recreation Area.

On this holiday weekend we discovered Fort Baker was uncrowded and beautiful. There was a simply spectacular view of San Francisco and a unique perspective of the Golden Gate Bridge. There was plenty of animal life to keep us entertained, and from the look of things, the fishing was good. It was a fine day....