Arizona Geological Survey at the University of Arizona

10/21/2026

15,000 years ago the Willcox Playa in southeast Arizona was home to Lake Cochise; with an area of 140 square miles and water depths to 46 feet. Today's playa, mantled by silts and clays, measures about 47 square miles with a perimeter of nearly 29 miles.

Google Earth serves up satellite imagery of Willcox Playa from 1985 to 2026. The resolution and spectral parameters of the satellite platforms have changed over time. Nonetheless, comparing early images, in this case from 1996, with recent images, 2026, suggests some alteration to the playa over time while showing that the playa surface is largely unchanged.

Images courtesy of Google Earth.

10/20/2026

From a published paper by Floyd & others (2026), “Area of Mogollon Highlands burned between 1985 and 2022. Study locations in Prescott National Forest shown in insert (triangles).” “During 1985–2022, 775 fires were identified in the region (Figure 6) with an average size of 4055 ha (SD = 14,481 ha)”.

Citation: Floyd & 4 others, 2026, A Little-Known Piñon from the Mogollon Highlands: Natural History of Pinus × fallax in the Prescott National Forest, Arizona, USA. Journal of Natural Areas, v 46 (4), p. 359-370 https://doi.org/10.3375/2162-4399-46.4.9

10/19/2026

The Utah Geological Survey has done a masterful job identifying geologic hazards of Utah and Arizona’s Glen Canyon National Recreational Area and environs. The paper contains dozens of images including this one showing the prevalence of seismicity (earthquakes) in southern Utah and northern Arizona. Geologic hazards addressed include: landslides, floods, rockfall, piping, erosion and wind-blown sand, expansive soil and rock, gypsiferous soil and rock, collapsible soil, liquefaction, earthquakes, and radon.

Graphic CAPTION: Figure 42. Earthquake epicenters, major Quaternary faults (red lines), Intermountain Seismic Belt (ISB), and Northern Arizona Seismic Belt (NASB) in relation to the Glen Canyon study area. Epicenter locations from the Arizona Earthquake Information Center (2016) and University of Utah Seismograph Stations (2020) earthquake catalogs.

Citation: Knudsen and 3 others, 2020, Geologic Hazards of the Bullfrog and Wahweap High-Use Areas of Glen Canyon National Recreation Area, San Juan, Kane, and Garfield Counties, Utah, and Coconino County, Arizona. Utah Geological Survey Special Study SS-166. https://geology.utah.gov/publication-details/?pub=ss-166

10/18/2026

Thirteen miles north of Lake Havasu, AZ, the Colorado River bisects a block of Pliocene gneiss-clast megabreccia (Tmgn). On the California side of the image, Cretaceous-age biotite granodiorite crops out extensively. The entire block is in the footwall of the Chemehuevi detachment fault as shown in the cross section by Howard & others (2013). https://ngmdb.usgs.gov/Prodesc/proddesc_98124.htm

Image: Annotated Goggle Earth image of Colorado River corridor north of Lake Havasu, AZ. Geologic map of the same area by Howard & others (2013). Geologic cross section of the same area by Howard & others.

Citation: Howard, K.A., John, B.E., Nielson, J.E., Miller, J.M.G., and Wooden, J.L., 2013, Geologic map of the Topock 7.5' quadrangle, Arizona and California. U.S. Geological Survey SIM-3236, Map scale 1:24,000.

10/17/2026

10/16/2026

Last week, six research scientists from our Mapping and Geohazards groups attended the annual meeting of the Geological Society of America in Denver. Their presentations covered a range of topics that demonstrates some of the breadth of our research here at AZGS. You can read about the presentations and find links to the conference abstracts here:
https://azgs.arizona.edu/news/azgs-annual-meeting-geological-society-america

One of the highlights of the GSA meeting was that Ann Youberg received the honor of becoming a newly elected GSA Fellow (shown in the photo here). Congratulations to Ann, and to all who presented their research at this meeting!

10/16/2026

The Middle Jurassic Entrada Sandstone shown here looks like the bleached bones of a giant disarticulated dinosaur weathering out of stone. This exposure occurs on Navajo Nation lands just east of the AZ-NM border. The Entrada hosts a shallow, cylindrical depression locally referred to as the ‘belly button’. It’s about 125 ft * 115 ft wide and perhaps equally deep.

Erosion by water and wind clearly played a major role in sculpting the shape of the exposed sandstone. The ‘belly button’ appears to be a pothole, sometimes referred to as a keeper pothole because of the difficulty of ascending its steep walls.

Prominent rock units noted on the image – from youngest to oldest:
Jcs – Cow Springs Sandstone (Middle Jurassic)
Jeu – Entrada Sandstone (Upper sandy member; Middle Jurassic)
Jeml – Entrada Sandstone (Lower ledge; Middle Jurassic)

NOTE: The ‘belly button’ is located on Navajo Nation lands and would, I believe, require express permission of the Navajo Nation to approach.

Citation: Thaden, R.E., 1989, Geologic map of the Fort Defiance quadrangle, Apache County, Arizona, and McKinley County, New Mexico. U.S. Geological Survey GQ-1648, Map scale 1:24,000. https://ngmdb.usgs.gov/Prodesc/proddesc_1167.htm

Citation: Netoff, DI and Chan, MA, 2009, Aeolian activity at a giant sandstone weathering pit in arid south-central Utah. Earth Surface Processes and Landforms, v. 39, p. 99-108. https://onlinelibrary.wiley.com/doi/epdf/10.1002/esp.1697

10/15/2026

Get ready to ShakeOut, Arizona! Today is ShakeOut, an annual earthquake preparedness exercise to practice the Drop, Cover, and Hold On safety measure, the recommended action in the event that you experience earthquake shaking. Please register and visit the Great Arizona ShakeOut site for more information and resources on earthquake safety! 🌵🫨

At 10:15 am, wherever you are, please take one minute to Drop, Cover, and Hold On! Thank you for helping to make Arizona a more seismically resilient state!

Great Arizona ShakeOut:
https://www.shakeout.org/arizona/

Register:
https://www.shakeout.org/register/index.php?start=arizona

10/15/2026

Hurricane Simon as seen by NOAA’s VIIRS (Visible Infrared Imaging Radiometer Suite) in the early morning of 11 Oct. 2026. CAPTION: Atmospheric gravity waves generated by Hurricane Simon are visible via mesospheric airglow in this nighttime image acquired with the VIIRS (Visible Infrared Imaging Radiometer Suite) on the NOAA-21 satellite on October 11, 2026. NASA Earth Observatory/Michala Garrison.

By way of further explanation from NASA’s Earth Observatory post, “This nighttime image (above), acquired with VIIRS on the NOAA-21 satellite, shows atmospheric gravity waves radiating from the hurricane. These ripples form when latent heat released near the tropical cyclone’s eyewall drives strong convection, building tall cumulonimbus clouds with updrafts that can send waves into the stratosphere and mesosphere.”

To see the entire story, go to https://science.nasa.gov/earth/earth-observatory/hurricane-simon-lurks-off-the-mexican-coast/ .

10/14/2026

The jet-black Clarksdale slag pile resides on ~51 acres of land adjacent to the Verde River. The slag is a byproduct of copper smelting of ore from the United Verde copper mine, Jerome, Arizona, and comprises a mixture of metal oxides and silica (SiO2). The fan-shaped slag pile weighs in at ~21 million tons and rises ~ 90 ft above the surrounding terrain. The Clarkdale smelter, from which the slag was produced, operated between 1915 and 1950.

As of Sept. 2022, the Searchlight Minerals Corp. was exploring metallurgical strategies for harvesting gold from the Clarkdale slag pile. FYI, nearby Cottonwood, AZ, has its own, smaller slag pile.

Images: Fan-shaped Clarksdale slag pile on Arizona’s Verde River. 1) An on-edge view of the slag pile adjacent to a railroad trestle.