Welcome to the Cal Geographic Report – we look forward to sharing news and updates of the biogeography and geomorphology of California’s living landscapes.
Today we will cover news and announcements from the US Geological Survey, the California Geological Survey and from the California Department of Fish and Wildlife (AKA Cal Fish and Game). Also in this and each episode of the Cal Geographic Report, we will encapsulate a few recent select scientific studies investigating California’s physical geography and biogeography.
Latest Geology and Tectonics news from CGS and USGS:
All volcanos monitored by the USGS California Volcano Observatory are at the Normal Alert level today. From north to south these include:
Cascades subduction complex volcanics:
Medicine Lake Volcano
Mount Shasta
Lassen Volcanic Center
Mendocino Triple Junction slab window/Mendocino Crustal Conveyor complex:
Clear Lake Volcanic Field
Basin and Range extensional tectonic complex:
Mono Lake Volcanic Field
Mono-Inyo Volcanic Crators
Long Valley Caldera
Mammoth Mountain
Ubehebe Crators
Coso Volcanic Field
Southern San Andreas Fault tectonic and transtensional complex:
Salton Buttes
Lets look at the most recent earthquakes in California, registered on the calvo website as well, within the last two week and then the last two hours:
Last Two Weeks = for the past two weeks we will not list all earthquakes, as there are many, but will take a look at broad geographic and tectonic patterns:
There are hundreds of small earthquakes along the entire length of the San Andreas Fault from the Salton Trough to the Mendocino Triple Junctions. I wont call them clusters, but the largest groupings of quakes in the last two weeks are centered in the southern region of the San Andreas Fault, and the Transverse Mountains, or Big Bend region. Going south to north there is a quiet patch, or gap in earthquake activity on the SAF from the Carrizo Plain area north to around Parkfield.
There have been several small earthquakes, magnitude 2.2 and below, along the Maacama fracture zone between Cloverdale and Laytonville to the north, in the past two weeks. The Maacama is a deep shear zone which forms the primary plate boundary between the North American and Pacific plates in northern California. Our article, The Mendocino Triple Junction: Tectonics, Evolution, and Structure covers this topic in more detail, and can be found here.
The largest earthquakes in the past two weeks are a part of what appears to be a cluster directly north of Susanville and northeast the Lassen Volcanic Complex. This is an interesting area tectonically because it is at the geomorphic intersections of the Cascades volcanic complex, the Basin and Range extensional basins, and the Modoc Plateau.. I’m going to guess these quakes have to do with the Cascades tectonic and volcanic region. I can’t find the name of a fault. The largest earthquake appears to be a 4.9 magnitude on December 31st, and is shallow at about five km deep.
In the past two hours there have been multiple small earthquakes registering below 2.0 in magnitude in the region of the geothermal plant activities at The Geysers, in Sonoma and Lake Counties, as usual. There was a 4.17 magnitude earthquake also registered in this area of human caused geothermal and seismic activity two days ago.
Here are some Basic Earthquake Behavior Notes to Consider from Cal Geographic:
Magnitude is the total energy released by an earthquake – not how the earthquake energy was released. Magnitude is determined by calculating the area (or length) of the fault that slipped, by the amount that area of the fault slipped, by the elastic properties of the crust.
Intensity of an earthquake is how an earthquake is felt, and that is different than the magnitude. Intensity depends on how the energy is released. The energy of an earthquake can be released in different ways.
Here are some of the key physical elements of earthquake energy release:
-Acceleration (how fast in G’s/G-force the crust accelerates from 0 G’s. It can be a slow acceleration producing a more rolling earthquake, or petal-to-the-metal fast acceleration for more violent shaking)
-Direction of travel
-Geologic environment/conditions
Our complete post on Basic Earthquake Behavior Notes with references is linked here
The California Geological Survey has released maps and reports for new revised earthquake zones in the following areas:
Affecting the city of Half Moon Bay and the counties of San Mateo and Santa Cruz, and the cities of Arcadia, Glendale, La Canada Flintridge, Monrovia, Pasadena, and Sierra Madre, and the county of Los Angeles. Affecting the cities of Palo Alto and Ridgecrest, the towns of Portola Valley and Woodside, and the counties of Inyo, Kern, Los Angeles, San Bernardino, San Mateo, and Santa Clara. And Affecting the city of Santa Rosa and the county of Sonoma.
Earthquake Fault Zones are regulatory zones that encompass surface traces of active faults that have a potential for future surface fault rupture. These maps are released under the authority of the Alquist-Priolo Earthquake Fault Zoning Act (Alquist-Priolo Act) that was passed following the 1971 San Fernando earthquake. The Alquist-Priolo Act is a state law designed to reduce the hazard from surface fault rupture during an earthquake.
The California Geological Survey released official maps and reports of Seismic Hazard Zones in the following areas:
Affecting the cities of Sacramento, West Sacramento, Santa Rosa, Sebastopol, and Windsor, and the counties of Sacramento, Yolo, Contra Costa, Alameda, and Sonoma. And affecting the cities of Concord, Danville, El Cerrito, Hercules, Lafayette, Martinez, Pinole, Pleasant Hill, Richmond, San Pablo, San Ramon, and Walnut Creek.
Seismic Hazard Zones are regulatory zones that encompass areas that have a potential for future ground deformations caused by liquefaction or landslides. These maps are released under the authority of the Seismic Hazards Mapping Act that was passed following the 1989 Loma Prieta earthquake. The Seismic Hazards Mapping Act is a state law designed to reduce the hazards from soil liquefaction and landslides during an earthquake.
Here are the Latest Biogeography and Wildlife updates from the California Department of Fish and Wildlife (Cal Fish and Game):
California Endangered Species Act (CESA) candidacy was granted for Gerry’s curly-leaved monardella and Pacific pocket mouse. Commissioners found sufficient scientific information to warrant possible CESA listings.
Gerry’s curly-leaved monardella is considered one of California’s rarest plants and the Pacific pocket mouse was once thought extinct. Each face threats such as habitat loss due to development. These species will now receive CESA protections while a status review is underway for potential CESA listing.
Gerry’s curly-leaved monardella is an annual herb in the mint family (Lamiaceae) that occurs in the Camarillo and Las Posas Hills in Ventura County. Gerry’s curly-leaved monardella is restricted to soil derived from Las Posas sand. The species has been documented from just three occurrences with fewer than 500 individuals in total.
CDFW is seeking informed comments and data from the public regarding Gerry’s curly-leaved monardella, and respectfully requests that data and comments be submitted before February 2, 2026, to allow sufficient time to evaluate this information during the status review period. Submit comments and general information on the petitioned action to CDFW’s Native Plant Program by email at NativePlants@wildlife.ca.gov, and include “Gerry’s curly-leaved monardella” in the subject line.
Further methods of submitting comments and data are linked here.
In a move to protect Red abalone populations that have suffered drastic population decline, the California Fish and Game Commission (Commission) at its Dec. 10-11 meeting extended the red abalone recreational fishery closure 10 years.
California’s red abalone population suffered a drastic decline, approximately 85%, following the 2014 kelp forest collapse triggered by a marine heatwave. The loss of kelp greatly contributed to this decline and the increase in purple sea urchin densities prevent kelp recovery, abalone’s primary food source. CDFW will be supporting abalone restoration through the development of a statewide red abalone restoration plan that will include robust and adaptive strategies to support abalone populations.
The Commission also approved listing Bear Lake buckwheat (Eriogonum microtheca var lacus-ursi) as an endangered species under the California Endangered Species Act (CESA) and received the California Department of Fish and Wildlife’s (CDFW) status review report for mountain lion in the central coast and southern parts of California.
The California Department of Fish and Wildlife (CDFW) announced that juvenile Coho salmon were spotted in a tributary of the Russian River in Mendocino County by a Pinoleville Pomo Nation water specialist — the first observation confirming natural reproduction of Coho in the Russian River’s upper basin since 1991.
To help the species continue to thrive, Pinoleville Pomo Nation and CDFW partnered for a rescue effort when it was discovered that these juvenile fish had become stranded in an isolated and drying pool. Teams used nets to collect two Coho, three Chinook, 146 steelhead and hundreds of other native and introduced fish species.
Highlights from Scientific Research Papers covering California’s physical geography and biogeography:
In the paper, Driving Processes of the Niland Moving Mud Spring: A Conceptual Model of a Unique Geohazard in California’s Salton Sea Region, author, Bary J Hibbs, of California State University, Los Angeles describes:
The Niland Moving Mud Spring, located near the southeastern margin of the Salton Sea, represents a rare and evolving geotechnical hazard. Unlike the typically stationary mud pots of the Salton Trough, this spring is a CO2-driven mud spring that has migrated southwestward since 2016, at times exceeding 3 m per month, posing threats to critical infrastructure including rail lines, highways, and pipelines. Emergency mitigation efforts initiated in 2018, including decompression wells, containment berms, and route realignments, have since slowed and recently almost halted its movement and growth. This study integrates hydrochemical, temperature, stable isotope, and tritium data to propose a refined conceptual model of the Moving Mud Spring’s origin and migration.
A key external forcing may be the 4.1 m drop in Salton Sea water level between 2003 and 2025, which has modified regional groundwater hydraulic head gradients. This recession likely enhanced lateral groundwater flow from the Moving Mud Spring area, potentially facilitating the migration of upwelling geothermal gases and contributing to spring movement. No faults or structural features reportedly align with the spring’s trajectory, and most major fault systems trend perpendicular to its movement. The hydrologically driven model proposed in this paper, linked to Salton Sea water level decline and correlated with the direction, rate, and timing of the spring’s migration, offers a new empirical explanation for the observed movement of the Niland Moving Mud Spring.
Hibbs, B.J. 2025. “Driving Processes of the Niland Moving Mud Spring: A Conceptual Model of a Unique Geohazard in California’s Eastern Salton Sea Region” GeoHazards 6(59).
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The authors of the paper “Formation and evolution of the Pacific‐North American (San Andreas) plate boundary: Constraints from the crustal architecture of northern California,” advance the ongoing efforts to unravel and comprehend the multidimensional and evolving mechanics of the Mendocino Triple Junction tectonic complex. This monumental picture comes into sharper focus, as stated here:
The northward migration of the Mendocino triple junction (MTJ) drives a fundamental plate boundary transformation from convergence to translation; producing a series of strike‐slip faults, that become the San Andreas plate boundary. We find that the 3‐D structure of the Pacific plate lithosphere in the vicinity of the MTJ controls the location of San Andreas plate boundary formation. At the time of initiation of the Pacific-North America plate boundary (∼30 Ma), the sequential interaction with the western margin of North America of the Pioneer Fracture Zone, soon followed by the Mendocino Fracture Zone, led to the capture of a small segment of partially subducted Farallon lithosphere by the Pacific plate, termed the Pioneer Fragment (PF).
Since that time, the PF has translated with the Pacific Plate along the western margin of North America. Recently developed, high-resolution seismic-tomographic imagery of northern California indicates that (a) the PF is extant, occupying the western half of the slab window, immediately south of the MTJ; (b) the eastern edge of the PF lies beneath the newly forming Maacama fault system, which develops to become the locus for the primary plate boundary structure after approximately 6–10 Ma; and (c) the location of the translating PF adjacent to the asthenosphere of the slab window generates a shear zone within and below the crust that develops into the plate boundary faults. As a result, the San Andreas plate boundary forms interior to the western margin of North America, rather than at its western edge.
Furlong, K. P., et al. 2024. “Formation and evolution of the Pacific‐North American (San Andreas) plate boundary: Constraints from the crustal architecture of northern California.” Tectonics 43:1-23
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Excerpts from, Geology of the Mokelumne paleochannel at the Miocene Zoo, Sierra Nevada foothills, California,USA, include:
“The Mokelumne paleochannel is one of a series of East-West-oriented, Eocene to late Miocene paleochannels that provide constraints on the topographic and tectonic evolution of the Sierra Nevada range. One of the largest fossil troves in California, hereafter referred to as the “Miocene Zoo,” was recently discovered in the Miocene Mehrten Formation, in the lower reaches of the Mokelumne paleochannel in the western Sierra Nevada foothills.”
“Here, we focus on the geologic setting of the Miocene Zoo by creating and compiling a digital map, contour maps, and series of measured sections; we also characterize tephras exposed at the fossil site.”
“The series of measured sections shows that the fossil site lies within a network of braided channels in the axis of the Mokelumne paleovalley, while nonfossiliferous overbank deposits lie in what was the shallowest part of the paleochannel.. We infer that the fossiliferous tuffaceous sandstones were rapidly deposited in flooding events accompanying explosive volcanic eruptions, while the pumices may have been briefly stored and later remobilized.”
“The stratigraphy and the abundance of tephras at the fossil site may indicate that the flora and fauna were buried by flooding triggered by explosive eruptions. We also infer that remobilization of silica from the tephras played a crucial role in fossilization..”
Swarner, H. et al. 2025. “Geology of the Mokelumne paleochannel at the Miocene Zoo, Sierra Nevada foothills, California, USA.” GSA Special Papers 563
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This paper has it all: geomorphology, marine isotopic stages, stratigraphic taphonomy, and some charismatic mega fauna mixed in:
New evidence for eolian activity and mammoths on Santa Rosa Island prior to the Last Glacial Maximum, explains:
Sea-level fluctuations due to the growth and decay of continental ice sheets of the Quaternary exert a strong influence on geologic processes along coastlines. The California Channel Islands are no exception to this, and many studies have been conducted that focus on the extremes of these glacial-interglacial cycles, such as the last glacial period (marine isotope stage [MIS] 2) and the last interglacial period (MIS 5). Far less attention has been paid to intermediate time periods between these extremes, such as MIS 4.
Here, we present two very different geologic records from this time period that show how sea-level change affected the nature of sedimentation on the northern shore of Santa Rosa Island.
On the northwestern coast of Santa Rosa Island, thick eolian sediments accumulated between ~80 ka and ~45 ka due to a lowered sea level that exposed carbonate-rich skeletal sands that had accumulated during the last interglacial period. On the central part of the northern coast of Santa Rosa Island, thick alluvial sediments were deposited between 80 ka and 47 ka, similar to the time of eolian sedimentation to the west.
A mammoth tusk discovered within these deposits is only the third stratigraphically controlled mammoth fossil on the Channel Islands that dates prior to MIS 2. Its discovery adds to the evidence that mammoths migrated to the Channel Islands from mainland California prior to the Last Glacial Maximum.
Muhs, D.R., et al. 2025. “New evidence for eolian activity and mammoths on Santa Rosa Island prior to the Last Glacial Maximum.” Western North American Naturalist 85(2):119–140
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The ascendant arboreal inventories executed within the crown of a Sitka spruce for the study, Epiphyte diversity, abundance, and distribution in an old Sitka spruce crown, tell us:
Preserving biodiversity in remaining old-growth forests is a high priority for many land managers. To this end, we inventoried the diversity, abundance, and distribution of epiphyte species in one 318-year-old, 86 m tall Picea sitchensis tree on the north coast of California. In 39 plots, we recorded species present and mean percent cover for each species. Our findings include the following: 1) 68 epiphyte species were found in this one tree; 2) epiphyte diversity increased with height; 3) lichens had the highest diversity of all epiphyte classes; and 4) mosses had the highest percent cover of all epiphyte classes. These findings highlight the capacity for old trees to serve as reservoirs of biodiversity in younger forests. Kerhoulas, L.P., et al. 2019. “Epiphyte diversity, abundance, and distribution in an old Sitka spruce crown.” Evansia 36(1):12-22
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Increased brain size of the dwarf Channel Island fox (Urocyon littoralis) challenges “Island Syndrome” and suggests little evidence of domestication
Although changes in overall body size during species’ island adaptation is a well-established phenomenon, there are mixed findings regarding how brain size changes within resource-limited insular environments. Work on this issue has focused on fossil species and herbivores, with limited studies on carnivores and extant island species. Here, we aim to close this knowledge gap and expand our understanding of brain size evolution by examining the relative brain size of the extant island canid, the Channel Island fox (Urocyon littoralis) amongst its six island-specific subspecies and in comparison to its larger mainland relative, the gray fox (Urocyon cinereoargenteus).
Our endocranial analysis found that foxes across five of the islands have a moderately higher relative brain size in comparison to the gray fox, with only the second smallest, most geographically isolated island, San Nicolas, exhibiting reduction. No significant differences in encephalization were found between sexes within any subspecies. These findings suggest that the selective pressures driving reduced body size on islands may not outweigh the adaptive benefits of increased brain size, with the exception of highly resource-constrained environments such as on San Nicolas.
Disparity in brain size among the three southern islands and the increased encephalization of San Clemente and Santa Catalina foxes compared to the mainland gray fox further suggests that although humans may have facilitated transport of the southern island foxes, true domestication was likely not practiced. Broadly, this research indicates that brain size reduction is not a straightforward trait of island adaptation, and changes in insular species’ brain size will vary in conjunction with island-specific selective pressures.
Schoenberger, KA, et al. 2025. “Increased brain size of the dwarf Channel Island fox (Urocyon littoralis) challenges “Island Syndrome” and suggests little evidence of domestication.” PLoS One 20(8)
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And from our last biogeographic highlight for January, 2026:
Mechanical thinning and prescribed fire benefit bumble bees and butterflies in a northern California conifer forest:
Land managers across western North America are increasingly treating forests with mechanical thinning and prescribed fire to reduce stand density, with the aims of reducing wildfire risks and generating conditions that better align with historic forest structure. The effects of these treatments on invertebrates in forests is poorly understood, especially over longer time scales.
We tested for effects of three forest treatments on butterfly and bumble bee abundance and species richness in a ponderosa pine and white fir forest in northern California, USA, that was treated systematically two decades prior to our surveys.
The forest treatments included: mechanical thinning that selected for large diameter trees, thinning for a more pine dominated stand, thinning for pine dominance combined with prescribed fire, and control areas without any treatments. The most substantial difference in vegetation structure stemming from the past treatments was reduced forest overstory and greater flowering plant richness in all treatments relative to control.
Butterfly and bumble bee richness was greater in all treatment types relative to control, though not always significantly so. Butterfly abundance was significantly greater in all treatments relative to control, and bumble bee abundance was significantly greater in pine treatments relative to control. Bumble bee and butterfly richness and abundance were most strongly positively related to greater plant species richness.
Overall, it appears that bumble bees and butterflies in our study area generally benefited from the changes in forest structure that were induced by each of the three treatments, and those benefits persisted for decades.
Cole, J.S., et al. 2025. “Mechanical thinning and prescribed fire benefit bumble bees and butterflies in a northern California conifer forest.” Forest Ecology and Management 588(122758)
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Thank you for listening – We look forward to further explorations and investigations of the biogeography and geomorphology of California’s Living Landscapes
