Field-trip guides to selected volcanoes and volcanic landscapes of the western United States

The US Geological Survey has just published Field-trip guides to selected volcanoes and volcanic landscapes of the western United States Scientific Investigations Report 2017-5022. Links to separate chapters are found at

Here is the table of contents:


The North American Cordillera is home to a greater diversity of volcanic provinces than any comparably sized region in the world. The interplay between changing plate-margin interactions, tectonic complexity, intra-crustal magma differentiation, and mantle melting have resulted in a wealth of volcanic landscapes.  Field trips in this guide book collection (published as USGS Scientific Investigations Report 2017–5022) visit many of these landscapes, including (1) active subduction-related arc volcanoes in the Cascade Range; (2) flood basalts of the Columbia Plateau; (3) bimodal volcanism of the Snake River Plain-Yellowstone volcanic system; (4) some of the world’s largest known ignimbrites from southern Utah, central Colorado, and northern Nevada; (5) extension-related volcanism in the Rio Grande Rift and Basin and Range Province; and (6) the eastern Sierra Nevada featuring Long Valley Caldera and the iconic Bishop Tuff.  Some of the field trips focus on volcanic eruptive and emplacement processes, calling attention to the fact that the western United States provides opportunities to examine a wide range of volcanological phenomena at many scales.

The 2017 Scientific Assembly of the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) in Portland, Oregon, was the impetus to update field guides for many of the volcanoes in the Cascades Arc, as well as publish new guides for numerous volcanic provinces and features of the North American Cordillera. This collection of guidebooks summarizes decades of advances in understanding of magmatic and tectonic processes of volcanic western North America.

These field guides are intended for future generations of scientists and the general public as introductions to these fascinating areas; the hope is that the general public will be enticed toward further exploration and that scientists will pursue further field-based research.



Critical mineral resources of the United States

The U.S. Geological Survey has just published a new assessment of mineral resources vital to our modern economy: Critical mineral resources of the United States—Economic and environmental geology and prospects for future supply, Professional Paper 1802

Edited by:Klaus J. Schulz , John H. DeYoung Jr. , Robert R. Seal II , and Dwight C. Bradley

You can download the entire book (148 Mb) and/or individual chapters here:


The book consists of two introductory chapters and 20 chapters which each discuss the geology, mineralogy, and occurrence of specific mineral commodities. Note that the U.S. is entirely dependent on imports for 20 critical minerals (see page 6 of this publication for a chart: )

The following map from PP1802 shows where the U.S. gets minerals for which we are at least 50 percent dependent on imports.


The first chapter in PP1802 justifies the need for this report as follows:

The global demand for mineral commodities is at an all time high and is expected to continue to increase, and the development of new technologies and products has led to the use of a greater number of mineral commodities in increasing quantities to the point that, today, essentially all naturally occurring elements have several significant industrial uses. Although most mineral commodities are present in sufficient amounts in the earth to provide adequate supplies for many years to come, their availability can be affected by such factors as social constraints, politics, laws, environmental regulations, land-use restrictions, economics, and infrastructure.

This volume presents updated reviews of 23 mineral commodities and commodity groups viewed as critical to a broad range of existing and emerging technologies, renewable energy, and national security. The commodities or commodity groups included are antimony, barite, beryllium, cobalt, fluorine, gallium, germanium, graphite, hafnium, indium, lithium, manganese, niobium, platinum-group elements, rare-earth elements, rhenium, selenium, tantalum, tellurium, tin, titanium, vanadium, and zirconium. All these commodities have been listed as critical and (or) strategic in one or more of the recent studies based on assessed likelihood of supply interruption and the possible cost of such a disruption to the assessor. For some of the minerals, current production is limited to only one or a few countries. For many, the United States currently has no mine production or any significant identified resources and is largely dependent on imports to meet its needs. As a result, the emphasis in this volume is on the global distribution and availability of each mineral commodity. The environmental issues related to production of each mineral commodity, including current mitigation and remediation approaches to deal with these challenges, are also addressed.

See also:

American non-fuel mineral production 2016

This article notes: The value of all non-fuel minerals produced from U.S. mines was $74.6 billion, a slight increase over production in 2015. “ Domestic raw materials and domestically recycled materials were used to process mineral materials worth $675 billion. These mineral materials were, in turn, consumed by downstream industries with an estimated value of $2.78 trillion in 2016.” Nevada was ranked first with a total mineral production value of $7.65 billion, mainly from gold. Arizona came in second in total production with a value of $5.56 billion and first in U.S. copper production.

Arizona’s Proterozoic Geology Revealed: Geologic maps of Phillip Anderson

From the Arizona Geological Survey:

Phil Anderson (Ph.D., University of Arizona) had a genius for mapping and interpreting the Proterozoic geology, tectonics, and mineral deposits of the Southwest. Unfortunately, his mapping was never made public, until now.

From the mid-1970s to the early 1990s, Phil traversed Arizona’s Transition Zone visiting and studying nearly every exposure of Proterozoic rocks. He described this work in his 1986 dissertation, ‘The Proterozoic tectonic evolution of Arizona’, and two subsequent papers from the Arizona Geological Society’s Digest 17, but he did not disclose his geologic maps. He issued, instead, small-scale, state-wide overviews of the distribution of Proterozoic rocks.

Phil passed away in Payson, Arizona, in Feb. 2012. In Sept. 2017, Donna Smart, Phil’s widow, donated Phil’s geologic map products and files – his life’s work – to the Arizona Geological Survey. Steve Reynolds (ASU Earth and Space Science Exploration) then organized and led a team of geoscientists in salvaging, reviewing, and selecting Anderson’s geologic maps to release as ‘The Philip Anderson Arizona Proterozoic Archive.

According to Reynolds and others (2017), the “Precambrian geologic maps of the Bradshaw Mountains, Central Arizona” represents the most significant collection of geologic maps ever released for the Proterozoic of Arizona. The Bradshow Mountains contributed map includes the following elements.

  • Reynolds & others (2017) contextualizing Anderson’s contribution to the Proterozoic of Arizona;
  • 11 geologic topographic quadrangles (1:24,000) from central Arizona’s Bradshaw Mountains, with key and legend;
  • A suite of geologic, structural, and tectonic illustrations;
  • 9 sub-regional geochemical plots;
  • 2 papers (totaling 150 p.) authored by Phil Anderson and published in the Arizona Geological Society’s Digest 17.
  • This is the first of a suite of Anderson geologic map products that we plan to release. The remaining Anderson collection comprises dozens of other topographic maps with original geologic observations and notes regarding structures and mineralogy. It will take several hundred hours to review, process, and prepare these materials for release.

    In the meantime, researchers working in the Proterozoic of Arizona’s Transition Zone are advised to reach out to the AZGS with specific requests for information.

    Acknowledgments. We thank Donna Smart for preserving and donating Phil Anderson’s geologic research. We thank, too, David Briggs (President) and the Arizona Geological Society Executive Committee for their generous permission to include Phil’s two papers from AGS Digest 17.


    Anderson, Phillip, 1986, The Proterozoic tectonic evolution of Arizona; Tucson, University of Arizona, unpublished PhD dissertation, 416 pages.

    Anderson, Phillip, 1989a, Proterozoic plate tectonic evolution of Arizona, in Jenney, J.P., and Reynolds, S.J., 1989, Geologic evolution of Arizona: Tucson, Arizona Geological Society Digest 17, p. 17 – 55.

    Anderson, Phillip, 1989b, Stratigraphic framework, volcanic plutonic evolution, and vertical deformation of the Proterozoic volcanic belts of central Arizona, in Jenney, J.P., and Reynolds, S.J., 1989, Geologic evolution of Arizona: Tucson, Arizona Geological Society Digest 17, p. 57 -147.

    Reynolds, S.J, Conway, F.M., Johnson, J.K., Doe, M.F., Niemuth, N.J., 2017, The Phillip Anderson Arizona Proterozoic Archive. Arizona Geological Survey Contributed Report CR-17-D, 2 p.

    On a personal note: I had the opportunity of working with Phil on a project of evaluating the United Verde mine, at Jerome. Arizona. The ore is hosted by Precambrian volcanic rocks. For a description of that deposit type, see my post

Arizona’s Monsoon Season Drives Earth Fissure Activity

This article is re-posted from the Arizona Geological Survey e-magazine. Article by Michael Conway.

See original:

Geoscientists agree, there is no such thing as an earthquake season. The tectonic forces producing earthquakes are inured from changes in meteorological or astronomical conditions; the latter involves fluctuation in gravitational forces due to the position of Earth’s Moon.

Arizona does, however, have an earth fissure season. A season when earth fissures are more likely to first appear or undergo renewed activity. Central and southeastern Arizona’s earth fissure season accompanies the onset of torrential rainfall of the summer monsoon, from mid-June to late September, with most precipitation occurring from mid-July to mid-August.

In southern and western Arizona, Cochise, La Paz, Maricopa, Pima and Pinal Counties all host earth fissures. In these five counties, we‘ve identified nearly 30 discrete earth fissure study areas, each with its own history, and comprising a collective 170 miles of mapped fissures and an additional 180 miles of reported but unconfirmed fissures. (Why unconfirmed? Three principal reasons: 1) ground disturbance has effectively masked the fissure; 2) built infrastructure now covers the fissure; 3) the feature was incorrectly identified as a fissure initially.)

Figure 1: Locations of study
Figure 1. The locations of earth fissure study areas: Apache Junction, Chandler Heights, Tator Hills and Three Sisters Buttes. Individual fissure study areas are bounded by turquoise polygons.

Release of 4 revised earth fissure maps

Each monsoon season finds the AZGS’ mapping team in the field addressing new leads and revisiting fissures with a history of activity. Mapping results are compiled on existing earth fissure study area maps, which are then revised, re-versioned, and released online at the interactive Natural Hazards in Arizona site. At the same time, we release an updated ESRI spatial data file (.shp) and Google Earth KMZ file, ‘Locations of Mapped Earth Fissure Traces in Arizona’, versioned to the date of release, in this case 06 Nov. 2017.

This year we are releasing revised maps for four earth fissure study areas (Figure 1):

Two of these, Apache Junction and Chandler Heights, have largely shifted from agricultural lands to residential or industrial use lands, markedly increasing the hazard and risk that accompanies fissuring.

Fissure activity ranges widely within and between study areas. Not all fissures are created equal; and not all fissures display activity each monsoon season. Most study areas retain some active fissures that either display slow incremental expansion, or dramatic episodic growth powered by eroding sheet flow accompanying torrential rains; sheet flow fans across the valley surface as a thin sheet of water spilling into open fissures eroding sidewalls and causing gullying.

Existing fissures frequently capture numerous drainages leading to incision (headcutting) on the up-channel side. Fissures often form orthogonal to the natural drainage direction, so channels and washes intersected by the fissure deliver water during and after rains.

With reduced groundwater harvesting and waning subsidence, fissures may transition from active to inactive status. When this occurs, they become sediment traps for wind- and water-borne sediments – clays, silts and sands – that subsume the fissure, masking its diagnostic morphology – a wide open throat, steep to inclined sidewalls and a hummocky, irregular base. Reactivation of dormant, partially filled earth fissures, may occur if heavy runoff, coupled with even modest land subsidence that produces tensional forces sufficient to reopen the fissure, counters the ‘healing’ process, leading to a wider and more deeply incised fissure.

Apache Junction: Case Study of a Reactivated Fissure

The Apache Junction earth fissure study area map was first released in April 2008. Over the past several years AZGS Earth Fissure manager Joe Cook has revisited the Apache Junction virtually, via Google Earth, and physically to examine new or reactivated earth fissures. According to Cook, ‘there’s about 0.8 miles of new fissures in Apache Junction since April 2008. Many of the new fissures formed parallel to existing fissures or connected gaps in formerly discontinuous fissures.’

On the morning of July 24, 2017, following heavy rains on the late evening and early morning hours of 23-24 July, nearly 320 feet of fresh fissure opened near West Houston Ave., Apache Junction (Figure 2). This new feature is part of a larger fissure zone that stretches for more than 2 miles from near the junction of Baseline and Meridian Roads to south of West Guadalupe Road (Figure 2a). The fissure complex tunnels below streets, state trust land, private property, and large power lines.

Figure 2: Houston Road area
Figure 2. Houston Road area ~ 3 miles south of Apache Junction, Arizona. A) Overview of Houston Road area impacted by fissuring on 23-24 July 2017; b & c (1) Houston Road closed due to road failure at site of fissures; d (2) Collapsed parking lot undermined by fissure; e (3) open fissure immediately north of Houston Road.  Red traces represent mapped continuous or discontinuous fissures; green traces represent reported but unmapped earth fissures.

According to Joe Cook’s report; ‘The fissure cracked West Houston Ave and an open void was visible beneath the road through a collapsed pothole. The road was closed to vehicle traffic immediately, but additional road collapse occurred over the days and weeks that followed. Large open depressions approximately 5-15 feet across and up to 8 feet deep, partially filled with collapsed material, were visible on private property to the south of Houston Ave. These open depressions were connected by parallel cracks beginning at Houston Ave to the north. Hairline cracks continued south of the southern-most depression for approximately 80 feet. Locally, a void space was visible below the hairline cracks indicating a strong potential for additional collapse.’

‘North of Houston Ave, the new fissure paralleled numerous, active and inactive, older fissures across the undeveloped desert floor. Additional reactivation and collapse along previously mapped fissures was observed beneath the powerlines in the southern part of the Apache Junction Study area.’

‘The cause for collapse of the fissure beneath Houston Ave is probably related to years of subsurface erosion along a buried earth fissure trace which intercepts rainwater from numerous drainages captured by the open portion of the fissure north of Houston Ave. During heavy rain events a substantial volume of floodwater is delivered to the fissure in a drainage ditch adjacent to the north side of W Houston Ave. Waning flow in this drainage ditch was observed to be pouring into the open fissure on the morning of July 25, 2017. No flow in the drainage ditch was observed downstream of the intersection with the earth fissure. The water draining into the fissure was not visible along the fissure anywhere else; water poured into the fissure in a free fall of about 8 feet before disappearing to unknown depths. Void space for further collapse must be substantial, which suggests that continued collapse following heavy rains is possible.’

By August 15, 2017 the collapsed portion of the fissure within the private property south of Houston Ave had been filled, presumably by the owner. But additional damage was evident, and the collapsed section of Houston Ave. remained closed.

Tator Hills: Case Study of a Fresh Fissure

Over the past several years, Tator Hills in southern Pinal County displayed the greatest fresh fissure activity of the four study areas (Figure 3). Imagery served by Google Earth shows that between Mar. 2014 and Dec. 2014, a mile-long, north-south trending earth fissure unzipped about 13 miles south of Arizona City. Sometime after March 2016, the fissure extended an additional ¾ mile to the south. The appearance of this fresh, 2-mile long fissure in an area of modest land subsidence ~ 1 inch (3 cm) annually over the past decade, and otherwise lacking active fissure formation since the early 1990s, was surprising (Cook, 2017).

Figure 3: Tator Hill Fissure
Figure 3. Fresh section of an earth fissure exposed in Tator Hills study area, Pinal County. a Bird’s-eye view from a DJI Phantom 3 drone operated by B. Gootee.  b Photo showing sharp, well-defined sidewalls and hummocky fissure floor. c Drone flying in fissure.

Applying drone technology to fissures. In Jan. 2017, AZGS geoscientists captured a real-time synoptic view of the newest Tator Hills fissure using a DJI-PhantomTM Drone. AZGS research scientist Brian Gootee piloted the drone and captured videos at 2.7K horizontal resolution, as well as 100s of high resolution, 12 Mb static JPEG images. The latter were stitched together using AgiSoft PhotoScanTM software and analyzed using both AgiSoft PhotoScanTM and ESRI’s ArcGISTM.

At our AZGS Youtube channel, the Tator Hills fissure videos have been viewed an astounding 780,000 times! See Drone technology examining an earth fissure or  Drone video of a fresh earth fissure, Tator Hills, Arizona.

The drone’s bird’s-eye view yielded a suite of derivative products – oblique orthoimagery, relief/slope map, digital elevation model (DEM), and topographic maps with contour interval of 1- to 2-feet (Figure 4) – that afford a fresh view of fissure geometry, structure, and topography that may yield new insights into the formative and evolutionary processes of fissures.

Figure 4: Drone Products
Figure 4. Derivative products from drone study of the Tator Hills earth fissure.

Chandler Heights and Three Sisters Buttes.  Since release of earlier mapping, we documented subtle changes in some fissures at Chandler Heights (2016), Maricopa County, and Three Sisters Buttes (2012), Cochise County. Chandler Heights infamous ‘Y-Fissure’, so called because of its Y-shaped geometry, remains active but the dramatic reopening and lateral extension observed in previous years has not recurred over the past several years. Nonetheless, the ‘Y-Fissure’ remains of great interest, in part because it winds through neighborhoods in east Queen Creek.

Agriculture is the economic engine that drives Cochise County.  The Three Sisters Buttes study area lies several miles southeast of Willcox Playa. Groundwater withdrawal and concurrent basin subsidence continues there unabated and from May 2010 to April 2017, maximum subsidence in the basin reached 9.8 – 15.7 in; 5 to 15 times greater than subsidence observed in the Tator Hills. In rural Cochise County, fissures chiefly threaten roads and pipelines and road signs warning of fissures is a common sight (Figure 5).

Some Observations & Final Thoughts

For the foreseeable future, earth fissures remain a geologic hazard in central and southeastern Arizona. With urban and suburban areas aggressively expanding into former agricultural areas, county and municipal planners may anticipate new and renewed incidents of costly and potentially hazardous impacts, as evinced by the recent damage to the W. Houston Rd. and nearby industrial plant in Apache Junction.

The state of earth fissures in Arizona. Nonetheless, there is hope on the horizon for a diminished threat from earth fissures. According to a recent blog post by hydrologist Brian Conway (Arizona Dept. of Water Resources), ‘Land subsidence rates within the Phoenix and Tucson Active Management Areas (AMAs) have decreased between 25% and 90% compared to the 1990s. This is a result of decreased groundwater pumping, increased groundwater recharge, and recovering groundwater levels in the two AMAs.’

Controlling groundwater pumping reduces basin subsidence, which should in turn re-establish hydrostatic equilibrium across impacted basins, thereby reducing the extensional stresses that lead to fissure formation.

Since 2007, systematic mapping of fissure study areas in Maricopa, Pima and Pinal Counties has uncovered few new earth fissures. Moreover, many fissures mapped between 2007 and 2009 showed physical evidence of having formed years or decades before. It could well be that the rate of earth fissure formation in most study areas reached its apex in the latter quarter of the 20th century. If so, land managers in these impacted areas should anticipate seeing fewer new fissures forming and, perhaps, waning reactivation of existing fissures.

In Cochise County, where groundwater pumping and basin subsidence continues unabated, we anticipate new fissures forming annually and existing fissures reopening.

Note of caution. There could be a substantial time-lag between reduced pumping, waning subsidence rates, and the end of new or renewed fissuring. By way of example, subsidence in the Tator Hills area has slowed substantially since the latter quarter of the 20th century. From 2004 to 2017, total subsidence proximal to the 2-mile long fissure was between 1.6 to 3.2 inches; a magnitude of subsidence that seems inconsistent with the formation of a 2-mile long fissure. This fissure may have formed years before, only to break the ground surface in 2014.  This could be true of concealed fissures in other study areas, too. We strongly recommend that civil authorities, farmers, contractors, and the public remain on the alert for the sudden emergence of rogue, outlier fissures.

Final Thoughts. The AZGS fissure mapping team continues to monitor earth fissure study areas, both virtually, via Google Earth and fresh National Agriculture Imagery Program (NAIP) imagery, and physically by returning to study areas. We confer regularly with county and municipal authorities regarding reports of reactivated or new fissures. Last, we remain aware of the potential of fissures forming in areas where the imbalance between groundwater harvesting and recharge leads to measurable basin subsidence, such as in agricultural lands of Cochise County and the McMullen Valley of Maricopa and La Paz Counties.


Arizona Land Subsidence Group, 2007, Land Subsidence and Earth Fissures in Arizona: Research and Informational Needs for Effective Management: Arizona Geological Survey Contributed Report CR-07-C, 29 p.

Conway, B., 2017, That sinking feeling: state-of-art technology at work on Arizona subsidence finds that you’re not imaging it. Arizona Geology Blog, 27 July 2017.

Cook, J.P., 2017, Discovery of a large earth fissure in the Southern Picacho Basin, Pinal County, Arizona. Arizona Geological Survey Open-File Report, OFR-17-01, 7 p., 1 appendix.

Cook, J.P. 2017, Internal report on fissuring in the vicinity of W. Houston St., Apache Junction, Pinal County.

Harris, R.C., 1999, Field Guide to Earth Fissures and other Land Subsidence Features in Picacho Basin. Arizona Geological Survey Open File Report, OFR-99-26, 55 p.

Schumann, H.H., and Cripe, L.S. (1986). Land subsidence and earth fissures caused by groundwater depletion in Southern Arizona, U.S.A. In A.I. Johnson, L. Carbognin & L. Ubertini (Eds.], Proceedings of the 3rd International Symposium on Land Subsidence, Venice, Italy, 19-25 March 1984 (pp. 841-851). International Association of Hydrological Sciences, Publication 151.

Slaff, S. (1993). Land Subsidence and Earth Fissures in Arizona.  Arizona Geological Survey Down-to-Earth Series #3, 30 p.

Geologic Field Guides to the Southeastern Picacho Mountains and Picacho Peak, Pinal County, Arizona

If you drive Interstate 10 between Tucson and Phoenix, about half way you pass between the Picacho Mountains (on the northeast side) and Picacho Peak (on the southwest side). Picacho Peak State Park is a frequent destination for picnics, rock climbing, and viewing spring wildflowers.

The Arizona Geological Survey has recently made available for free download Geologic Field Guides to the Southeastern Picacho Mountains and Picacho Peak. (Link)

From the guide:

The Picacho Mountains consist largely of a compositionally diverse suite of Laramide to middle Tertiary biotite granite, muscovite granite, and heterogeneous to gneissic granite. At the southern end of the range, most of the crystalline rocks have been affected by middle Tertiary mylonitic deformation. Mylonitization is inferred to have accompanied normal faulting and ascent of the bedrock from mid-crustal depths to near the Earth’s surface. [Mylonitization is modification due to dynamic recrystallization following plastic flow.]

Ascent occurred in the footwall of a moderate to low-angle normal fault commonly known as a “detachment fault”. The crystalline rocks of the Picacho Mountains are part of the footwall of a south- to southwest-dipping detachment fault that is exposed only at the base of a small klippe of volcanic rock on a hill top in the southeastern Picacho Mountains. [A klippe is an isolated block of rock separated from the underlying rocks by a fault.]

Picacho Peak, itself, looks like the remnant of a volcano. However, it is an erosional remnant of volcanic rocks that were displaced from over the Picacho Mountains by a detachment fault.

Picacho Peak is composed of multiple andesitic lava flows interbedded with thin sequences of medium- to thin-bedded, well-sorted, medium- to coarse-grained arkosic sandstone and granule sandstone. See the guide for detailed descriptions.

Earth fissures occur in the Picacho Peak area due to groundwater withdrawal and soil compaction. (See: Earth Fissure Map of the Picacho & Friendly Corners Study Area)

For some spectacular views, see a drone flight around Picacho Peak (3 minutes):

See also:

Picacho Peak weather station – how not to measure temperature

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











Rocks in the Chiricahua National Monument and Fort Bowie National Historic Site

The Arizona Geological Survey has made available for free download a 48-page booklet which explains geologic features of two areas of southeastern Arizona. This well-illustrated booklet is intended for the layman but is also interesting to experienced geologists.

The Chiricahua mountains are known for their thousands of rock pinnacles formed in volcanic rocks by weathering during the last glacial epoch. In a previous article, I explain “The Explosive Geology Of The Chiricahua Mountains.”



The new booklet provides photos and descriptions that allow you to find many volcanic features along major roads and trails in the monument. None of these features are designated by markers along the trail.

The geology of Fort Bowie is quite different and consists of sediments and granite intrusive rocks.

As described in the booklet:

“Fort Bowie was built to guard Apache Pass, a natural passage between the Dos Cabezas and Chiricahua Mountains that connects the San Simon and Sulphur Springs Valleys. The

dependable springs, including Apache Spring, that have attracted humans to this narrow passage for thousands of years are also the result of geology, specifically the Apache Pass fault.”

The booklet starts out by describing the past 30 million years of geologic history which includes plate tectonics and volcanism – the processes which gave rise to the features visible today.

The features of the Chiricahua Mountains are put in context as follows:

“The landscape of Chiricahua National Monument, like that of much of the Earth’s surface, is a complex mosaic of large and small geologic features. Some of these features were produced by processes that were more active in past geological time but have now slowed or ceased. Other features are the result of past and currently active processes; only a few owe their origin solely to recently active processes. Welded tuff, fiamme, surge beds, fossil fumaroles, and the dacite caprock, for example, were all produced during the eruption of the Turkey Creek caldera, about 27 million years ago. Some joints and spherulites formed as the ash sheet cooled. Other joints and the region’s mountain ranges and intervening basins are the result of Basin and Range faulting during the period 25 to 5 million years ago. Willcox Playa, talus cones, pinnacles, and slot canyons were produced by processes that were more active during the wetter, cooler climate of the glacial epochs from 1.6 million to 10,000 years ago. Tafoni, rock varnish, lichens, case-hardened surfaces, chicken heads, exfoliation shingles, horizontal ribs, solution ponds and the rounded form of the columns are all forming today. Unraveling the evolution of such complex landscapes makes geology a particularly challenging science.” If you are unfamiliar with some of the names of features, read the booklet.

URL to the booklet:


New releases from the Arizona Geological Survey – September 2017

The Arizona Geological Survey is in the process of digitizing both new and older geological reports and releasing them to the public as free downloads.

This month they released a classic work by E.D. Wilson et al.: “Arizona Lead and Zinc Deposits, Part 1″ which was originally published in 1950. (146 p., 19 plates)

Download it here:

They have also released an index of mining properties in Santa Cruz County, Arizona (100 pages).


Previous releases available for free down include:

(Note: some of these links take you first to my review of the papers.)


A guide to the geology of the Sedona & Oak Creek Canyon area of Arizona

A Guide to the Geology of the Santa Catalina Mountains

A Guide to the Geology of Organ Pipe Cactus National Monument and the Pinacate Biosphere Reserve

A Guide to the Geology of the Flagstaff Area

A Guide to Geology of Petrified Forest National Park

A Guide to Oak Creek-Mormon Lake Graben

AZGS Guides to Northern Arizona Geology

AZGS field guides to Arizona Geology

Eldred Wilson’s Proterozoic Mazatzal Revolution Arizona


History of the Ajo Mining District, Pima County, Arizona

History of the Warren (Bisbee) Mining District

History of the San Manuel-Kalamazoo Mine, Pinal County, Arizona

Recovery of Copper by Solution Mining Techniques

Superior, Arizona – An Old Mining Camp with Many Lives

History of the Copper Mountain (Morenci) Mining District

History of Helvetia-Rosemont Mining District, Pima County, Arizona

History of the Silver bell mining district



Houston’s long history of flooding

Houston, Texas, seat of Harris County, has a long history of flooding because the city was built on a flood plain. The deluge generated by hurricane Harvey in August, 2017, is only the latest episode.

Houston lies within a coastal plain about 50 miles northwest of Galveston. The area has very flat topography which is cut by four major bayous that pass through the city: Buffalo Bayou, which runs into downtown and the Houston Ship Channel; and three of its tributaries: Brays Bayou, which runs along the Texas Medical Center; White Oak Bayou, which runs through the Heights and near the northwest area; and Sims Bayou, which runs through the south of Houston and downtown Houston. The ship channel goes past Galveston and into the Gulf of Mexico.

The land around Houston consists of sand, silt, and clay deposited by local rivers.

The sedimentary layers underneath Houston ultimately extend down some 60,000 feet, with the oldest beds deposited during the Cretaceous. Between 30,000 feet and 40,000 feet below the surface is a layer of salt, the primary source of salt domes which dot the metropolitan area. Since salt is more buoyant than other sediments, it rises to the surface, creating domes and anticlines and causing subsidence due to its removal from its original strata. These structures manage to capture oil and gas as it percolates through the subsurface. [source]

Groundwater pumping also causes subsidence in parts of the city. (See: Geologists find parts of Northwest Houston, Texas sinking rapidly )

Hurricane damage in Houston:

As described by the Harris County Flood Control District (HCFCD) [link]:

When the Allen brothers founded Houston in 1836, they established the town at the confluence of Buffalo and White Oak Bayous. Shortly thereafter, every structure in the new settlement flooded. Early settlers documented that after heavy rains, their wagon trips west through the prairie involved days of walking through knee-deep water. Harris County suffered through 16 major floods from 1836 to 1936, some of which crested at more than 40 feet, turning downtown Houston streets into raging rivers.

Houston was flooded during the September, 1900, hurricane which wiped out Galveston.

In December of 1935 a massive flood occurred in the downtown Houston as the water level height measured at Buffalo Bayou in Houston topped out at 54.4 feet which was higher than Harvey. There have been 30 major floods in the Houston area since 1937 when the flood control district was established in spite of construction of flood control measures.

In June, 2001, Harris County suffered widespread flooding due to hurricane Allison. According to HCFCD, before leaving the area, Allison would dump as much as 80 percent of the area’s average annual rainfall over much of Harris County, simultaneously affecting more than 2 million people. When the rains finally eased, Allison had left Harris County, Texas, with 22 fatalities, 95,000 damaged automobiles and trucks, 73,000 damaged residences, 30,000 stranded residents in shelters, and over $5 billion in property damage in its wake.

Some climate alarmists are claiming that global warming has played a part in the flooding produced by hurricane Harvey. Dr. Roy Spencer debunks that notion here and here. Storms of or greater than Harvey’s magnitude have happened before. Storm damage is not due entirely to weather. Some is due to local infrastructure.

It all boils down to the luck of the draw: if you choose to inhabit a flood plain, you will get wet from time to time.

P.S. Prior to Harvey, which made landfall as a Category 4 storm, the U.S. had gone a remarkable 12 years without being hit by a hurricane of Category 3 strength or stronger. Since 1970 the U.S. has only seen four hurricanes of Category 4 or 5 strength. In the previous 47 years, the country was struck by 14 such storms.

Eldred Wilson’s Proterozoic Mazatzal Revolution Arizona

The Arizona Geological Survey has just made available for download papers by Eldred Wilson, a pioneer of Arizona geology.

Eldred Dewey Wilson & the Proterozoic ‘Mazatzal Revolution’

Study area map of Wilson (1937)

In 1937, geologist Eldred Dewey Wilson coined the phrase ‘Mazatzal Revolution’ to describe mountain building along the western edge of the North American craton. While the Mazatzal Revolution occurred in the Proterozoic – more than 1.6 billion years ago – it continues to influence Arizona geology and mineral exploration to this day. Wilson’s 1937 Ph.D. research is now available online for the first time.

In about 1920, twenty-two-year old Eldred Dewey Wilson joined a handful of geologists – N.H. Darton, Carl Lausen and Olaf P. Jenkins, among them – wrestling with the complex geology of the rugged mountains of southern and central Arizona. Wilson was an assistant geologist at the Arizona Bureau of Mines and working on his M.S. thesis, ‘The Mazatzal Quartzite, a new pre-Cambrian formation of central Arizona’ at the University of Arizona. In 1924 Wilson was promoted to geologist at the Bureau, where he remained, with a short leave of absence to begin his doctoral research in 1931-1932 at Harvard University, until his death in 1965.

Wilson set out in 1930 to address, ‘the chief features of pre-Cambrian regional structure within part of central Arizona’, for his Ph.D. dissertation – ‘‘The Pre-Cambrian Mazatzal Revolution in Central Arizona’. His field area included the Mazatzal Mountains, Pine Creek, eastern Tonto Basin or northern Sierra Ancha, Del Rio, and the southern Black Hills areas, all of which contained extensive outcrops of Proterozoic-age rocks. Wilson concluded from his observations of the field relationships of rocks and structures that the ‘principal features of regional structure originated from a great pre-Cambrian crustal disturbance’, which he called the ‘Mazatzal Revolution’.

Wilson’s ‘Mazatzal Revolution’ was an early contribution to deconstructing the processes responsible for the geology of central Arizona. He noted, ‘The subparallel folds, thrust faults, and imbricate, steeply dipping reverse faults clearly resulted from intense north­west-southeastward regional compression. The transverse faults are believed to have been formed, also during the compression, by shearing normal to the trend of the folds.’

Wilson hypothesized, too, that, ‘structural weaknesses inherited from the Mazatzal Revolution may have influenced the localization of many of Arizona’s prevailingly north­eastward-trending veins and the pattern of the Tertiary Basin and Range faulting.’ The orogenic Mazatzal Revolution continues to impact Arizona geology today.

E.D. Wilson ca. 1960s.

Reynolds & Others (2013) on Eldred Dewey Wilson’s contribution to Arizona geology. Wilson published a number of important papers on Arizona geology. According to Reynolds and others (2013), Eldred D. Wilson provided the first geologic map and cogent discussion of the geology and mineral resources of southern Yuma County: “Wilson mapped this hitherto unknown area of southwestern Arizona from 1929-1932. In the process, he discovered a new set of mountains that had been overlooked by previous geologists and explorers. He named this range the Butler Mountains after G. M. Butler, former Director of the Bureau and Dean of the College of Mining and Engineering (Wilson, 1931). Wilson was the first person to describe and map the geology of a large number of mountain ranges in southwestern Arizona. The data from Wilson’s 1933 geologic map were incorporated into the 1969 state geologic map.”

See James T. Forrester and Richard E. Moore’s ‘Memorial to Eldred Dewey Wilson 1898-1967’ for more about the life and times of Dr. Wilson.

Note: AZGS thanks an anonymous patron who arranged at his/her own expense with Harvard University to scan Wilson’s dissertation and secure copyright permission from Dewey Wilson to re-release Dr. Wilson’s work as CR-17-C.

Forrester, J.T. and Moore, R.E., 1965 Memorial to Eldred Dewey Wilson 1898-1967. Geological Society of America Bulletin, V. 76, p. 187-191.

Reynolds, S., Spencer, J.E., Richard, S.M., Pearthree, P.A. 2013, The Geological Exploration of Arizona: The Role of State and Federal Surveys and the Geologic Map of Arizona, Arizona Geology Magazine, Winter 2013.

Wilson, E.D., 1922, The Mazatzal Quartzite, a new pre-Cambrian formation of central Arizona. Univ. of Arizona M.S. thesis, 40 p.

Wilson, E.D., 1937, The Pre-Cambrian Mazatzal Revolution in Central Arizona. Ph.D. Dissertation, Harvard University, Cambridge, MA, 335 p.

This post is reblogged from Arizona Geology