Arizona Geological Survey at the University of Arizona

06/19/2026

The Gila River is the principal tributary of the San Carlos Reservoir on the San Carlos Apache Indian Reservation, Arizona. Meager snowfall in the Gila River watershed in 2025-2026 has shrunk the reservoir to about 400 acre-feet, a fraction of it’s capacity.

Authorities closed the reservoir on 5 June 2026 after low oxygen levels choked the fish population, comprising largemouth bass, black crappie, bluegill, catfish, rainbow and brown trout.

Source: NASA Earth Observatory, images by Michala Garrison, narrative by Adam Voilant.
https://science.nasa.gov/earth/earth-observatory/low-water-at-san-carlos-reservoir/

06/18/2026

“This photo shows an active fault in Flagstaff, northern Arizona. The red rock at the right side is Triassic Moenkopi Formation, about 245 million years old. The rock at left is probably Quaternary in age, aka the last few millions years. Fault movement has juxtaposed these two deposits of different age. This excellent exposure was excavated during construction of an apartment in 2020.” Source: AZGeology on Instagram.

Photo by Chad K. (AZGS)

06/17/2026

The Arizona Geological Survey (AZGS) was pleased to participate in the 118th Annual Meeting of the Association of American State Geologists (AASG), held June 6–11, 2026, in Harrisonburg, Virginia. The meeting brought together State Geologists and other state survey staff, the US Geological Survey (USGS), and other federal agency representatives, and geoscience leaders from across the United States to discuss national priorities, emerging geoscience challenges, and opportunities for collaboration among state and federal partners.

AZGS was represented by Director and State Geologist Phil Pearthree and AASG Associate Brian Gootee. They participated in technical discussions, committee meetings, strategic planning sessions, and field excursions focused on advancing the role of geological surveys in supporting energy development, critical mineral resources, groundwater sustainability, geologic hazards, geologic mapping, and public safety.

Founded in 1908, the AASG represents the State Geologists and Geological Surveys of the 50 states, Puerto Rico, and U.S. territories. AASG serves as a national forum for collaboration among state geological surveys and provides a unified voice on issues related to geoscience research, natural resources, hazards, mapping, and public policy. The organization works closely with federal agencies, including the U.S. Geological Survey (USGS), to coordinate programs and advocate for investments in geologic data, mapping, resource assessments, and hazard characterization.

Participation in AASG is particularly important for Arizona because many of the state's priorities—including energy security, geothermal resource development, critical minerals, groundwater management, geologic hazards, and geologic mapping—depend on strong partnerships with federal agencies and other state surveys. Through AASG, AZGS helps shape national geoscience initiatives, shares Arizona's expertise and challenges, and ensures that Arizona remains engaged in programs that provide funding for our projects as well as critical geologic data and scientific information to support informed decision-making.

AZGS appreciates the opportunity to collaborate with colleagues from across the country and to represent Arizona's geoscience interests at this important national gathering.

06/17/2026

Marshall Lake, situated 14 miles southeast of Flagstaff, Arizona, at 7,100 ft above sea level. The lake is carpeted in part by grass mats - thick, floating beds of aquatic vegetation and bulrushes. The individual pads ring the shoreline and are as much as 130 ft in diameter. When fully wetted the lake covers nearly 0.5 square miles. As often as not the wetted/grass surface covers only half of that. The lake sits on basalt flows (Pliocene-Miocene age) in a north-south trending graben (Ulrich & others, 1984; https://ngmdb.usgs.gov/Prodesc/proddesc_9245.htm).

Migratory waterfowl are seasonally abundant at Marshall Lake.

For more on Marshall Lake, including camping and seasonal information, visit the Coconino National Forest Marshall Lake website - https://www.fs.usda.gov/r03/coconino/recreation/marshall-lake .

06/16/2026

“Zonies” Head to San Diego – An invited post by Flagstaff-based geologist and educator Wayne Ranney.

When temperatures climb in the Sonoran Desert, many Arizonan’s head to San Diego and its cool, coastal breezes. Locals there have a (not always complimentary) name for us – Zonies! While the surf, sand and beach amenities draw many, those interested in geology find a variety of interesting rocks as well.

Point Loma is a popular destination with visitors and rises above a spectacular entrance to San Diego Bay. In 1542 Juan Rodriguez Cabrillo was the first European to sail into the bay and Cabrillo National Monument on Point Loma is named for him. The National Park Service operates a Visitor Center here and maintains a historic lighthouse. A statue of Cabrillo is also at the point and was given by the government of Portugal to California in commemorating their native son (in 1542 he was in the employ of the Spanish Empire).
A paved road leads from the lighthouse down to the Pacific Ocean side of the peninsula, where road cuts and beach erosion expose a sequence of Late Cretaceous marine rocks. In Photo 1, waves lash onto the Point Loma Formation, composed of thinly-bedded and moderately-indurated sandstone and mudstone, deposited in tidal, continental shelf, and deeper ocean environments (below the red line in the Photo 1). Overlying these is the Cabrillo Formation, forming the easily eroded slopes seen in that photo (both units have their type sections here). The Cabrillo Formation contains a large volume of cobble and boulder conglomerate, laid down in submarine fans. Excellent exposures are found in the road cuts leading down to the shore (Photo 2). The clasts within the Cabrillo Fm. were derived from the plutonic and volcanic rocks in the Peninsular Ranges to the east and a detailed paleogeography has been inferred by San Diego geologist-extraordinaire, Patrick Abbott. All photos by the author.

STRAT column for the San Diego Bay area showing the Point Loma and Cabrillo formations (courtesy of Macrostrat.org).

Abbott, Patrick L., 1999: The Rise and Fall of San Diego, Sunbelt Publications

06/15/2026

NEW! The U.S. Geological Survey has published a report and interactive map highlighting the mineral commodities of China’s mineral industries. Mineral resources include, antimony, coal, copper, phosphate, potash, mineral deposits, and mineral exploration sites. Also included are oil and gas production and recoverable resources.

Download at https://pubs.usgs.gov/publication/ofr20261018b

The report Abstract, “As part of the U.S. Geological Survey’s (USGS) mission to distribute global mineral information and analyze supply chains, this study provides a comprehensive review of the global significance of China’s mineral production and capacity in 2023. Of 77 mineral commodities in the USGS dataset, China produced 74 and was the world’s first- ranked producer for 39 of the 74. Compared to the high share of global mineral production, including up to 98 percent of global gallium production, the country’s share of global mineral reserves was relatively small, ranging from 20 percent (zinc ore) to 52 percent (tungsten ore). China’s imports of metal ores, slag, and ash accounted for 64 percent of global imports of such commodities by value. The country’s exports of base metals and articles of base metal accounted for 17 percent of the global exports. To help nongeographic information system users assess the spatial distribution of mineral mines, processing facilities, and ports for trades in China, this study created a geospatial (also called “georeferenced”) portable document format (GeoPDF) map. In addition, the GeoPDF contains mineral resource tracts (such as antimony, copper, potash, coal, and oil and gas), exploration sites, and energy infrastructure based on the preexisting USGS data.”

Citation: Chung, J., Neustaedter, E.R., Moon, J.W., Xun, S., and Textoris, S.D., 2026, Production of mineral commodities and geospatial map of the mineral industries and related infrastructure of China: U.S. Geological Survey Open- File Report 2026–1018, 1 map sheet, scale 1:17,500,000, 19-p. pamphlet, https://doi.org/ 10.3133/ ofr20261018.

06/14/2026

The source of the 0.60-million-year-old Fence Lake lava flow of eastern Arizona originates ~ 60 miles to the east in the Zuni-Bandera volcanic field of New Mexico. West of the AZ-NM border, the Fence Lake lava flow entered the drainage of the Zuni River near Jaralosa Draw. According to Laughlin and others (1993) the flow is approximately 90 feet thick. The top of the basalt flow is about 340 feet above the channel of the present-day Zuni River.

The Fence Lake lava is a tholeiitic basalt with olivine, clinopyroxene, plagioclase and minor iron-titanium oxides. The world’s ocean floors consist of tholeiitic basalts, making it the most common volcanic rock comprising Earth’s crust.

Citation: Laughlin and 8 others, 1993, Geochronology of Mount Taylor, Cebollita Mesa, and Zuni-Bandera volcanic fields, Cibola County, New Mexico. New Mexico Geology, v. 15, #4, p. 81-92. Download athttps://geoinfo.nmt.edu/.../nmg/15/n4/nmg_v15_n4_p81.pdf

06/13/2026

Rockhounding in Utah. Well done Utah Geological Survey.

Are you looking to explore rocks, minerals, fossils, or beautiful landscape rocks? Check out our web app! Tailor your search based on your interests and get detailed information, including location descriptions, land ownership, coordinates, directions, and vivid photos.

Remember, being a responsible rockhound means practicing good stewardship of the land. Be aware that, depending on your location and the type of land, you might need additional permits from state or local agencies. Always respect private property rights and avoid trespassing.–https://geology.utah.gov/apps/rockhounder/

06/12/2026

Shaped by movement on the active Hurricane Fault (Miocene to Holocene), the Hurricane Cliffs stretch ~155 miles from south of Grand Canyon to Cedar City, UT. Robert Biek, Utah Geological Survey, wrote a magnificent 12-p. note on the geology of the cliffs for Utah Geological Assn. Publication 48 (2019). You can download the report at https://www.giw.utahgeology.org/index.php/geosites/article/view/51/69

IMAGES: Figure 1. The six segments of the Hurricane fault zone, each of which has a different
rupture history and rate of long-term slip; arrows indicate segment boundaries. The three geosites described here lie at the northern end of the Anderson Junction segment. The fault continues north of Cedar City but that section was not part of the study of Lund and others (2007) from which this figure is taken.

PHOTO: View north-northwest along Hurricane fault zone just west of (Utah) State Route 9 (Biek 2019).

CROSS SECTIONS: “Cross sections through the Hurricane Cliffs between the La Verkin and Hurricane Overlooks. See figure 3 for section locations and figure 4 for rock unit names. Note that map (1:62,500) and cross sections (1:24,000) show different levels of detail and so do not match exactly. From Biek (2003).”

Citation: Biek, R.F., 2019, Hurricane fault, in Milligan, M., Biek, R.F., Inkenbrandt, P., and Nielsen, P., editors, Utah Geosites: Utah Geological Association Publication 48, 12 p., https://doi.org/10.31711/geosites.v1i1.51.

06/11/2026

Gordon Haxel (US Geological Survey retired) and colleagues recently provided AZGS with a excellent ‘Contributed Report’ of a field trip to the Gavilan Hills of SE-most California. The 29-p field guide is available for download at https://library.azgs.arizona.edu/item/AGCR-1767999258242-638.

From the, “Why the Gavilan Hills?” section:

“According to current tectonic models, much of southern California and southwest Arizona (Figs. 1, 2) is underlain by the Late Cretaceous (Laramide) Pelona-Orocopia-Rand Schist (PORS) subduction complex, “the best-known archive of shallow subduction on the planet” (Chapman 2016). Subduction was shallow in both depth and inclination. One part of this complex, the Orocopia Schist subduction channel of southwest Arizona, has attracted particular attention over the past decade, for two reasons. First, it is exposed unusually far inland from the present and late Mesozoic Cordilleran continental margin ... Second, Orocopia Schist in one area, Cemetery Ridge, uniquely includes well-preserved blocks of subducted oceanic-mantle peridotite (Haxel et al. 2014, 2018b, 2023).”

IMAGE Caption: (Fig. 24, p. 23) “View from Gavilan Hills, southeasternmost California, eastward into southwest Arizona, showing approximate locations of five exposures of Orocopia Schist along the Chocolate Mountains anticlinorium (§8; Figs. 1, 2, 22). Castle Dome Mountains, 45 km long, are largely early Miocene intermediate to silicic volcanic, subvolcanic, and hypabyssal rocks. Most volcanic rocks erupted from two large calderas exposed in and northeast of the northern part of the range (Grubensky and Bagby 1990; Grubensky et al. 1993, 1995). CDP, Castle Dome Peak; TP, Thumb Peak.

Citation: Haxel, G.B., Jacobson, C.E., and Epstein, G.S., 2025, Field trip to a Laramide shallow subduction channel: Orocopia Schist in the Gavilan Hills, southeasternmost California; with incidental localities for three blue minerals: Arizona Geological Survey Contributed Report CR-25-A, version 2.0, 29 p., map scale 1:32 000.