Ice Age Mammals of the San Pedro River Valley, Southeastern Arizona

If you had been in Southeastern Arizona eleven or twelve thousand years ago, it would look much different from today. The climate was cooler and wetter, and the rivers actually flowed. Also, you would encounter a suite of large mammals which became extinct in North America. These animals included horses, camels, mastodons, mammoths, long-horned bison, tapirs, shrub oxen, and ground sloths, which were preyed upon by dire wolves, jaguars, cougars, bears, the American lion, and man. (Horses and camels were re-introduced from Europe and Asia.)

We know this because remains of all these animals were found in several sites along the San Pedro River between Tombstone and Bisbee and at other sites in southern Arizona.

At the end of the last glacial epoch, climate became very unstable with the result that many of these megafauna became extinct in North America and the human Clovis culture dispersed. I go into greater detail on extinction hypotheses in my article “Cold case: What Killed the Mammoths?” linked below.

The Arizona Geological Survey published a paper about these animals in 1998 which has recently become available for free download:

Within this 32-page publication are drawings and brief descriptions of the animals and information about Clovis culture humans who hunted them. The paper describes how people hunted and speculates on causes of extinction.

According to AZGS:

Popular literature and illustrations often depict Clovis hunters using stone-tipped spears to attack full-grown mammoth. Archaeological evidence indicates, however, that they more often concentrated their efforts on calves and young adults, sometimes ambushing them near or at watering places. At the Lehner Mammoth Site bones of nine mammoths, all juveniles, were recovered. They were apparently trapped and killed in the stream bed where archaeologists uncovered their bones thousands of years later. The mammoth killed at the Naco Site was also a young adult.

Bison meat appears to have been popular among the Clovis people. At Murray Springs bones of eleven young bison were found along with bones of one mammoth. Both the mammoth and the bison were likely ambushed when they came to water.

Being so large and cumbersome to transport, a mammoth carcass was butchered where it fell. The presence of hearths at kill sites, such as Murray Springs and the Lehner Site, suggests that the hunters also ate some of the meat on the spot, perhaps roasting it as they proceeded with the butchering. Cut marks on bone surfaces, and broken cutting tools indicate that the meat was stripped from the carcass and transported to a nearby camp, where more of it could have been eaten or dried for future consumption.

See also:

Cold Case: What Killed the Mammoths?

A Very Brief History of Climate Change in the Sonoran Desert

Where the Glyptodonts roamed











New Release – AZGS field guides to Arizona Geology

The Arizona Geological Survey has just e-published field guides to Arizona geology. The 422-page series of illustrated guides is available for free download at

These guides were originally published as the proceedings of the 100th annual meeting of The Geological Society of America (GSA) was held in Phoenix, Arizona in October 1987. The newly available online guides are organized into separately downloadable sections.

One guide that may be of interest to laymen is “The Archaeological Geology of Paleo.-Indian Sites in Southeastern Arizona” which begins on page 212 of the Southern Arizona section. This paper discusses the late Quaternary geologic history preserved in the sediments in the San Pedro Valley and the Sulphur Springs Valley in southeastern Arizona . “These sediments are host to some of the oldest archaeological remains in North America.” Along the San Pedro River near Tombstone, “The Murray Springs Clovis site is unique in that it contains three distinct activity areas where a band of Clovis hunters killed a mammoth and several bison and occupied a small campsite during two or three brief visits 11,000 years ago. The buried occupation surface is clearly displayed in the arroyo walls as an erosional contact at the base of a distinctive black organic mat that preserved artifacts and extinct animal bones in their original position, and mammoth tracks, just as they were left 11,000 years ago.”

Here are the papers and guides:


Field-Trip Guide for Marble Canyon and Eastern Grand Canyon

Field Guide to the Lower Grand Canyon, from Peach Springs to Pierce Ferry

Geology of the Lower Grand Canyon and Upper Lake Mead by Boat–An Overview

Geology of the Grand Canyon – A Hike Through Time

Upper Holocene Alluvium of the Southern Colorado Plateau

Late Pleistocene Alluvium and Megafauna Dung Deposits of the Central Colorado Plateau

Late Cenozoic Volcanism in the San Francisco and Mormon Volcanic Fields

A Field Guide to the Jemez Mountains Volcanic Field, New Mexico

Stratigraphy, Correlation, and Tectonic Setting of Late Cretaceous Rocks in the Kaiparowits and Black Mesa Basins

Field Guide to Sedimentary Structures in the Navajo and Entrada Sandstones in Southern Utah and Northern Arizona


Late Paleozoic Depositional Systems, Sedona-Jerome Area, Central Arizona

Tectonic and Magmatic Contrasts Across a Two-Province Proterozoic Boundary in Central Arizona

Geomorphology and structure of the Colorado Plateau/Basin and Range Transition Zone


Land Subsidence and Earth-Fissure Formation in Eastern Phoenix Metropolitan Area, Arizona

Selected Hydrogeologic Problems in Central Arizona

The Archaeological Geology of Paleo-Indian Sites in Southeastern Arizona

Terraces of the Lower Salt River Valley in Relation to the Late Cenozoic History of the Phoenix Basin, Arizona

Late Cenozoic Deposits, Vertebrate Faunas, and Magnetostratigraphy of Southeastern Arizona

Caldera Structures Along the Apache Trail in the Superstition Mountains, Arizona

Field Guide to Lower- and Upper-Plate Rocks of the South Mountains Detachment Zone, Arizona

Structural Geology of the Rincon and Pinaleno Metamorphic Core Complexes, Southeast Arizona

Pinto Valley Copper Deposit

Tectonic Setting and Sedimentological Features of Upper Mesozoic Strata in Southeastern Arizona

Lower Cretaceous Coral-Algal-Rudist Patch Reefs in Southeastern Arizona


Paleoecology and Taphonomy of Recent to Pleistocene Intertidal Deposits, Gulf of California

Volcanic Structures and Alkaline Rocks in the Pinacate volcanic field of Sonora, Mexico

The Mesquite and Picacho Gold Mines: Epithermal Mineralization localized within Tertiary Extensional Deformation

Mesozoic Tectonics of Southeastern California

Field-Trip Guide to Parts of the Harquahala, Granite Wash, Whipple, and Buckskin Mountains,
West-Central Arizona and Southeastern California

Metamorphic Core Complexes, Mesozoic ductile Thrusts, and Cenozoic Detachments: Old Woman Mountains-Chemehuevi Mountains Transect, California and Arizona

Miocene Extension, Volcanism, and Sedimentation in the Eastern Basin and Range Province, Southern Nevada

Crustal Transect: Colorado Plateau-Detachment Terrane-Salton Trough

Flatulent Fauna Fables and climate

A story making the rounds is creating headlines such as the one in the ever credulous Arizona Daily Star: “Flatulent dinosaurs helped warm Earth, study says.” British researchers posit that the flatulence of herbivorous dinosaurs produced so much methane that it warmed the climate. The paper, published in Current Biology is summarized by the authors as follows:

Mesozoic sauropods, like many modern herbivores, are likely to have hosted microbial methanogenic symbionts for the fermentative digestion of their plant food. Today methane from livestock is a significant component of the global methane budget. Sauropod methane emission would probably also have been considerable. Here, we use a simple quantitative approach to estimate the magnitude of such methane production and show that the production of the greenhouse gas methane by sauropods could have been an important factor in warm Mesozoic climates.

If you read the story (full text here) you will find that the contention depends on many assumptions and rather extravagant extrapolation. The gassiest dinosaurs were the Sauropods which became abundant during the Jurassic Period about 150 million years ago. Global temperatures are estimated to have been 18 F warmer than today, but that warmth began in the preceding Triassic Period about 250 million years ago. There seems to be a timing problem. Also, the researchers estimate that the amount of methane produced by dinosaurs was similar to the amount produced today by livestock farming and industry, so why aren’t we warmer?

At the end of the paper, the researchers note as an attempted justification for their speculation:

 “Although dinosaurs are unique in the large body sizes they achieved, there may have been other occasions in the past where animal-produced methane contributed substantially to global environmental gas composition: for example, it has been speculated that the extinction of megafauna coincident with human colonization of the Americas may be related to a reduction of atmospheric methane levels.”

That references a 2010 paper in which the researchers estimated the amount of methane produced by mammoths and other large herbivores. They speculate that the arrival of humans in North America and the subsequent disappearance of these animals reduced methane emissions and led to an abrupt cooling period, the Younger Dryas, about 12,800 years ago.

At the end of the Younger Dryas, the global temperatures and atmospheric methane both rose rapidly. So where did the methane come from since those flatulent mammoths were no more? The mammoth fart theory fails to explain previous similar abrupt cooling and warming in the Older Dryas period and the Oldest Dryas period, nor a subsequent similar event about 8,200 years ago.

Both of these papers present interesting stories, but they both fail upon close inspection. Still, science is speculative and the stories make headlines and get the authors published.

See also(links updated):

Arizona Geological History Chapter 5: Jurassic Time

Ice Ages and Glacial Epochs

Research Review 3 Climate cycles and a Mammoth Mystery

Cold Case: What Killed the Mammoths

Mammoths, mastodons, saber-toothed cats, glyptodonts, and other great beasts roamed the land of North America, Europe, and Asia, until something happened about 12,000 years ago. Just what that something was, is subject to great debate. We will focus on the case in North America.

Hypotheses attempting to explain the extinctions include: The mammoth hunters “is wot done it”, disease, normal climate change at the end of the glacial epoch, and abrupt climate change caused by a big flood or a comet strike.

Here is what we do know. Humans (of the Clovis Culture) entered North America at least 13,500 years ago when abundant megafauna inhabited the land. The planet was warming up from the last glacial epoch and had reached temperatures similar to today. Between about 12,900 and 11,500 years ago there was an abrupt cooling episode called the Younger Dryas (after a small Arctic flower), during which global temperatures plunged, in a matter of decades, from temperate climes to near glacial conditions. It stayed cold for about 1,400 years then rapidly warmed again. During that time, most of the megafauna became extinct. Evidence of the human Clovis culture also disappeared.

That point in time about 12,000 years ago, the end of the Pleistocene epoch, is marked in many places with a “black mat” of rich organic material. Below the mat are abundant fossils of megafauna and artifacts of the Clovis culture. No such fossils and few, if any, Clovis artifacts are reported above the black mat.

A study of the black mat at 50 Clovis sites in North America found a “discrete layer with … magnetic grains with iridium, magnetic microspherules, charcoal, soot, carbon spherules, glass-like carbon containing nanodiamonds, and fullerenes with ET helium, all of which are evidence for an ET impact and associated biomass burning at 12.9 ka.”

Let’s examine the hypotheses: (more…)

Mesquite Trees Provide Food and a Pharmacy

The ethnobotany of Mesquite trees is extensive. The trees provide food, medicine, beverages, glue, hair dye, firewood, and furniture. Mesquites coevolved with large herbivores such as mammoths, mastodons, and ground sloths, which ate the pods and dispersed them widely. When these Pleistocene animals became extinct, mesquites retreated to flood plains and washes where water and weathering scarified the seeds and aided germination. The introduction of cattle helped to expand the range of mesquites once again.


Use as food

Mesquite beans are usually harvested after they turn hard and golden. Both the pods and the seeds (which are very tough) are ground into meal. The native people sprinkled the ground meal with a little water to form small, round cakes. Later, slices of dried cake were fried like mush, used to thicken stews, or eaten raw. The meal is also used as flour to make flat bread. Mesquite meal is gluten free.

The pods of mesquite beans are very sweet and the sweetness comes from fructose which doesn’t require insulin to be metabolized. The seeds contain about 35% protein, much more than soybeans. Mesquite pods contain about 25% fiber. Some research suggests that mesquite meal, with a low glycemic index of 25, helps regulate blood sugar.

Mesquite flour is used to make a refreshing drink. If allowed to ferment, a mixture of water and mesquite flour produces a fizzy alcoholic drink.

Mesquite flowers are collected and boiled to make tea. The flowers are also roasted and pressed into balls as another food source.

The pharmacy

The black tar or sap of mesquite trees can be boiled and diluted with water to make eye wash and an antiseptic for open wounds. It was also used on sore lips, chapped skin, as a sunburn lotion, and as a treatment for venereal disease.

A liquid made from boiling the inner bark of the tree was used as a laxative and as an emetic.

Tea made from mesquite leaves was used for headaches and stomach trouble. This tea also was used to cure conjunctivitis and to heal painful gums.

Other uses

The Pima Indians used the black tar as a hair dye. This involved boiling the tar and applying the mixture to the hair, covering the hair with mud over night, then thoroughly washing the next morning. Resin from the tree was used as glue to mend pottery, or when boiled and diluted, as paint for pottery. The inner bark of the tree was used for basketry.

General information

There are several species of mesquite trees. Within the desert southwest, the Velvet mesquite (Prosopis velutina), the Honey mesquite (Prosopis glandulosa), and the Screwbean mesquite (Prosopis pubescens) are most common. These deciduous plants form shrubs and trees up to 30 feet tall. The branches contain spines. Most of the roots of mesquite trees are within the upper three feet of soil where most of the oxygen and water are. However, mesquite roots can go very deep. The deepest live root, found in a copper mine, extended 160 feet below the surface.

If you collect fallen bean pods, you may notice small holes in the pods. These holes are made by bruchid beetles, which infested the fallen bean as larvae, when it was green and tender. The holes were made by the mature beetle getting out of the bean. Don’t worry, the beetles just add more protein. Another insect found commonly with mesquite trees is the Giant Mesquite Bug.

For a description of the common mesquite species see here.

For more natural history and photos, see here.

For recipes using mesquite, see here.

Research Review 3 Climate cycles and a Mammoth Mystery

What caused the extinction of Mammoths and other megafauna12,000 years ago? How is the position of the earth relative to the sun related to the glacial-interglacial cycles of our current ice age? These questions are explored by two research papers, one from the University of Arizona, the other from the University of California – Santa Barbara.

First up is the story from Santa Barbara.

The paper: “Links between eccentricity forcing and the 100,000-year glacial cycle” by geologist Lorraine E. Lisiecki examines the timing of glacial cycles relative to the position of the earth and the sun, published April 4 in Nature, Geoscience online (available only with a subscription). (Note: the press release from UCSB had some rather questionable statements, so I emailed Ms. Lisiecki and she kindly sent me the entire paper.)

Some background: The earth’s orbit around the sun varies from nearly circular to moderately elliptical on a cycle of 100,000 years. The tilt of the earth’s axis relative to the plane of the solar system (obliquity) varies between 22.1 and 24.5 degrees and back again on a cycle to about 41,000 years. This tilt produces the variation in seasons. (Currently the Earth is tilted at 23.44 degrees from its orbital plane.) The third major variation, precession, is the direction of the axis of rotation relative to the “fixed” stars. This is like the wobble of a gyroscope. This cycle is 21,000 to 26,000 years. All of these cycles impact the amount of solar radiation impinging on the planet.

The important point about Ms. Lisiecki’s research is that she found hard evidence linking these cycles to global temperature. Lisiecki examined sea sediment cores, representing a time frame of 5 million years, from 57 locations throughout the world. The temperature proxy used was the variation of the oxygen-18 isotope gleaned from calcite in foraminifera fossils. This is a common proxy used in investigation of past temperature. (Foraminifera are rice-grain-sized, one-celled animals that have a calcium carbonate shell. They were first recognized from Cambrian-aged rocks, 550 million year ago, and many species still exist today.) In the first part of our current ice age, the glacial-interglacial cycle was 41,000 years. But 800,000 years ago that cycle changed to 100,000 years. Lisiecki found statistically significant correlations between the proxy temperature data and the timing of eccentricity and obliquity cycles. The question remains about why and how the longer cycle overcame the shorter cycle and it points out that there is a natural instability in climate during ice ages. Lisiecki proposes that “internally driven climate feedbacks” are the source of the change to a 100,000-year glacial. She does not expand on what those feedbacks are.

Now, on to the mammoths.

At the end of the last glacial epoch about 14,000 years ago, North America, and other places sported megafauna. In Arizona there were three species of mammoths, mastodons, camels, horses, large bears, large saber-toothed cats, and a critter called the glyptodont, essentially a volkwagen-sized armadillo. There were also people hunting all these animals, people of the Clovis culture. And they all disappeared between 12,000 and 10,000 years ago. Many theories abound as to why. It is speculated that the Clovis people hunted mammoths to extinction, or they brought disease which decimated the populations. Perhaps it was the climate change of the new interglacial period than changed things too much.


Following the end of glacial conditions, the climate warmed to about what it is now. But there was a cold snap, a period called the Younger Dryas. About 12,900 years ago temperatures plunged within a few decades to near glacial conditions again. That cold snap lasted about 1,000 years, followed by abrupt warming. The beginning of the Younger Dryas is marked, in some places, by a thin layer of soot. There are remains of megafauna and Clovis people below that layer, but none above it. It is speculated that a comet exploded over North America and caused continent-wide fires. The resulting climate change caused the demise of the megafauna.

Research from the University takes exception to the comet theory. The paper: “The Murray Springs Clovis site, Pleistocene extinction, and the question of extraterrestrial impact” was published in the Proceedings of the National Academy of Sciences, March 2, vol. 107 no. 9.

“Some of the evidence for the recent hypothesis of an extraterrestrial impact that caused late Pleistocene megafaunal extinctions was based upon samples collected at Murray Springs, a Clovis archaeological site in southeastern Arizona.” The researchers examined the black sooty mat and also some magnetic microspherules which can have their origin on earth as well as in comets. The researchers did not find any iridium or radiation anomalies that are commonly associated with comets (but iridium can originate from volcanoes as well).

The UofA researchers say the black mat is the result of an algal bloom from moist soil, not soot from a fire. They explain the magnetic spherules as originating “in exhaust from vehicles and power plants” that were washed into the Murray Springs site. They found sooty material only at the campsites and say it was the result of camp fires. Nanodiamonds are found in the sooty layer also. The UofA researchers say, “A common ingredient of cosmic dust, nanodiamonds are constantly raining down onto the earth’s surface, rendering them unsuitable as unequivocal evidence of an extraterrestrial impact.”

In the end, however, the UofA researchers cannot rule out a cosmic event, but they say it is very unlikely. You can read the press release here:

Other research shows that decline of megafauna began before the Younger Dryas. So, what killed the mammoths? There is much speculation, but we still don’t know the reason for sure.

The mammoth mystery continues to intrigue.

Antarctic Ice Shelf Collapse Due to Waves

Research Review #1:

From time to time I will summarize new science research from recently published, or about-to-be published papers. Usually, notice of the research comes in the form of press releases from universities that are made available to the media. Here are some reports that the Arizona Daily Star apparently missed.

Antarctic Ice Shelf Collapse Possibly Triggered by Ocean Waves

Scripps Institution of Oceanography

Background: In the summer of 2007, Arctic sea ice melted more than it had previously. The media made much of that, but failed to mention that the same year, Antarctic sea ice reached the greatest extent ever recorded. You may also remember that in 2008, several large chunks of Antarctic sea ice broke off to become very large icebergs. The general media trumpeted this as evidence of global warming. Scripps has an alternative theory.

The research findings:

Storm-driven waves in the North Pacific break along the coastlines of North and South America where “they are transformed into very long-period ocean waves called ‘infragravity waves’ that travel vast distances to Antarctica.” The authors “propose that the southbound traveling infragravity waves may be a key mechanical agent that contributes to the production and/or expansion of the pre-existing crevasse fields on ice shelves, and that the infragravity waves also may provide the trigger necessary to initiate the collapse process.” “The study found that each of the Wilkins Ice Shelf breakup events in 2008 coincided with the estimated arrival of infragravity waves. The authors note that such waves could affect ice shelf stability by opening crevasses, reducing ice integrity through fracturing and initiating a collapse.”

Press release and photo:

Does Global Warming Threaten Alpine Ecosystems?

Research shows that the combination of genetic diversity within and among alpine species and the high diversity of micro-habitats in alpine terrain precludes any profound effects of warming on alpine species survival. See analysis from here:

The mammoths’ swan song revised

University of Copenhagen

The researchers claim that by using DNA in soil samples they found that mammoths existed back to between 10,500 and 7,500 years ago, and are therefore remained between 2,600 and 5,600 years after their supposed extinction from mainland Alaska. “Our findings show that the mammoth and the horse existed side by side with the first human immigrants in America for certainly 3,500 years and were therefore not wiped out by human beings or natural disasters within a few hundred years, as common theories otherwise argue.” The research does not address the ultimate cause of their disappearance.

Press release:

Team finds subtropical waters flushing through Greenland fjord

Woods Hole Oceanographic Institution

“Waters from warmer latitudes — or subtropical waters — are reaching Greenland’s glaciers, driving melting and likely triggering an acceleration of ice loss…”

Press release: