Geology of the Northern Sacramento Valley, California

California Department of Water Resources (DWR) | September 22nd, 2014

This study describes the complex geology of the northern Sacramento Valley, focusing on the Late Cenozoic geologic formations and structures that compose or influence the

This study describes the complex geology of the northern Sacramento Valley, focusing on the Late Cenozoic geologic formations and structures that compose or influence the valley’s fresh groundwater aquifer formations. The California Department of Water Resources (DWR) acquired geologic data from groundwater observation well drilling operations that were conducted in the valley over the last 15 years. Using the observation well drilling data, DWR evaluated and classified the lithology of the subsurface sediments, implemented petrographic sand provenance analyses on lithologic sediment samples, and reviewed associated geophysical logs from each bore hole. In addition, DWR conducted an extensive literature review of published and unpublished data and then integrated the data to produce this geologic report, map, and cross sections that describe the geology of the northern Sacramento Valley. Results from the lithologic logging, petrographic analyses, and data review show that the heterogeneous sediments of the northern Sacramento Valley’s most productive groundwater-bearing geologic formations, the Tehama Formation and the Tuscan Formation, intermix in the subsurface in various areas near the center of the valley. The results also show that toward the westward and eastward extents of the valley, the sediments of the formations become more unified in composition due to the proximity of their respective sediment source areas. However, because of the depositional environment of the geologic formations, sediment sizes within the formations can be discontinuous and intermittent in places, resulting in variable groundwater aquifer zones within the geologic formations. Additional data are needed to further define the northern Sacramento Valley aquifer system. Drilling and installing groundwater observation wells in areas of little or no data can provide the information needed to determine the extent and variability of the valley’s groundwater aquifers. Groundwater level data supplied by the observation wells can provide valuable information for monitoring aquifer conditions, for determining the change in groundwater levels over time, and for assessing the ability of groundwater to move through the geologic aquifer sediments. In addition, a textural analysis of formational sediments using lithologic cuttings and/or driller’s well logs could be performed to better identify aquifer production zones. In summary, the geology of the northern Sacramento Valley is diverse and has a widely varied historical sequence of earth-shaping events. It includes periods of time when much of the area was below sea level, multiple and distinct periods of volcanic activity, several periods of mountain building, and intermingled periods of massive erosion and deposition. Analyses of the data illustrate the heterogeneity of the groundwater-bearing geologic formations in the subsurface, and the intermixing of formational sediments toward the center of the northern Sacramento Valley, resulting in a region with great geologic and hydrogeologic complexity.

Gillnet Sampling Methods for Monitoring Status and Trends of Clear Lake Hitch in Clear Lake, Lake County, California

U.S. Geological Survey (USGS) | May 2nd, 2025

The Clear Lake Hitch (Lavinia exilicauda chi) is a minnow endemic to Clear Lake, Lake County, California. This species is listed as a threatened species under the Califor

The Clear Lake Hitch (Lavinia exilicauda chi) is a minnow endemic to Clear Lake, Lake County, California. This species is listed as a threatened species under the California Endangered Species Act and has been petitioned for listing under the United States Endangered Species Act. In 2017, the U.S. Geological Survey, in cooperation with the U.S. Fish and Wildlife Service, initiated a Clear Lake Hitch monitoring program to generate information annually on relative abundance and size structure.

Glaciers in California’s Sierra Nevada are likely disappearing for the first time in the Holocene

American Association for the Advancement of Science (AAAS) | October 1st, 2025

Mountain glaciers are sensitive climate indicators. Glaciers in the western United States are projected to disappear by 2100 CE, but whether they were previously absent i

Mountain glaciers are sensitive climate indicators. Glaciers in the western United States are projected to disappear by 2100 CE, but whether they were previously absent in the current interglacial (past 11,700 years) remains debated. Here, we present evidence that two of the largest glaciers in California’s Sierra Nevada near Yosemite National Park persisted throughout the Holocene. Cosmogenic in situ carbon-14 and beryllium-10 exposure dating in newly exposed proglacial bedrock indicates continuous Holocene cover, likely by ice. At a nearby smaller glacier, bedrock exposure-burial ages suggest glacier expansion at ~7 thousand years ago, earlier than previously recognized. Moraine exposure ages at these sites and the Sierra Nevada’s largest glacier are distributed across the past several thousand years, suggesting that glaciers were near their preindustrial extent for much of the late Holocene. These findings imply that a glacier-free Sierra Nevada is unprecedented since before the Holocene. Future alpine glacial environments in California are thereby likely a no-analog scenario within the current interglacial.

Gold Extraction Processes

Scientific American | October 31st, 1896

FROM very early times the ancients were attracted the beautiful color, the brilliant luster and the indestructibility of gold, and spared no pains in the endeavor to acqu

FROM very early times the ancients were attracted the beautiful color, the brilliant luster and the indestructibility of gold, and spared no pains in the endeavor to acquire it. In the code of Menes, who reigned in Egypt some 2,000 years before the time of Moses, the ratio of value between gold and silver is mentioned, one part of gold being declared equal in value to two and a half parts of silver, and it is, therefore, clear that the extraction of both metals from the deposits containing them must have been carried on before that time. It is indeed probable that gold was the first metal observed and collected, since it occurs in fragments of all sizes in loose sand, and the operations of collecting the larger pieces and melting them together are so simple. Among the rock carvings of Upper Egypt there are several illustrative of the art of washing auriferous sands by stirring and working them up by the hand in hollowed-out stone basins, and subsequently melting the gold in simple furnaces with the aid of mouth blowpipes. The earliest of these carvings is supposed to date back to about 2,500 B.C. However, in ancient times, gold appears to have been mainly derived from India, and that country continued to supply most of the gold used in Europe until the discovery of America by Columbus.

Groundwater dominates snowmelt runoff and controls streamflow efficiency in the western United States

Nature Portfolio (Springer Nature) | May 3rd, 2025

Hydrologic Modeling Goals and Objectives for Yolo County

Water Resources Association of Yolo County, California Department of Water Resources (DWR) | May 16th, 2002

The Water Resources Association of Yolo County (WRA) has entered into a Memorandum of Understanding (MOU) with the California Department of Water Resources (DWR) to coo

The Water Resources Association of Yolo County (WRA) has entered into a Memorandum of Understanding (MOU) with the California Department of Water Resources (DWR) to cooperatively investigate conjunctive use opportunities in Yolo County. As part of the MOU, DWR is assisting the WRA to develop goals and objectives for a combined groundwater and surface water model of Yolo County, including a modeling strategy. As DWR’s contractor, WRIME, Inc., in collaboration with the DWR, WRA, and other consultants with modeling experience/knowledge about Yolo County, conducted the modeling assessment study.

Hydrology, Hydraulics, and Water Management Technical Report

U.S. Bureau of Reclamation (USBR) | December 15th, 2014

This Technical Report describes pertinent hydrologic and hydraulic condition and water management operations for Shasta Lake, the Sacramento River, the Delta, and the CVP

This Technical Report describes pertinent hydrologic and hydraulic condition and water management operations for Shasta Lake, the Sacramento River, the Delta, and the CVP/State Water Project (SWP) service areas, under existing conditions, the No-Action Alternative, and the Action Alternatives for the SLWRI.

Importance of subsurface water for hydrological response during storms in a post-wildfire bedrock landscape

Nature Portfolio (Springer Nature) | June 29th, 2023

Improving the Health of California’s Headwater Forests

Public Policy Institute of California (PPIC) | September 18th, 2017

California’s headwater forests are not thriving under current management practices, and changes are needed to make them more resilient to periodic drought and long-term

California’s headwater forests are not thriving under current management practices, and changes are needed to make them more resilient to periodic drought and long-term climate change. More active management of these lands is needed to improve forest health, reduce the risk of major wildfires and pest infestations, and maintain the flow of benefits provided by this critical natural infrastructure. Decades of fire suppression, an emphasis on short-term management priorities, weather extremes, and a warming climate have set the stage for the decline in forest resilience. Two-thirds of the state’s surface water supply originates in these mountainous forests. California stands to lose timber production, wildlife habitat, recreational opportunities, and water supply if this vital natural infrastructure continues to decline. Management options exist—prescribed fire, managed wildfire, mechanical thinning, and forest pest treatments—that can help rebuild resilience in these forests and prepare them for a challenging future.

Instream Flow Studies for the Protection of Public Trust Resources: A Prioritized Schedule and Estimate of Costs

California State Water Resources Control Board (SWRCB) | February 18th, 2011

Chapter 5 of the 2009-10 Seventh Extraordinary Session (SB X7 1, Simitian) directs the State Water Resources Control Board (State Water Board) to submit to the Legislatur

Chapter 5 of the 2009-10 Seventh Extraordinary Session (SB X7 1, Simitian) directs the State Water Resources Control Board (State Water Board) to submit to the Legislature, by December 31, 2010, a prioritized schedule and estimate of costs to complete instream flow studies for two categories of rivers and streams, by two specific deadlines: 1) high priority rivers and streams in the Delta watershed that were not covered in the Board’s “Final Report on Development of Flow Criteria for the Sacramento-San Joaquin Delta Ecosystem” by 2012; and 2) all major rivers and streams outside the Sacramento River watershed by 2018. The definition of the two stream categories is ambiguous. There are a number of tributaries that are both in the Delta watershed and outside the Sacramento River watershed, including the San Joaquin, Calaveras, Cosumnes, and Mokelumne Rivers. The State Water Board interprets the first category to mean all Delta and Sacramento River tributaries not covered under the Board’s “Final Report on Development of Flow Criteria for the Sacramento-San Joaquin Delta Ecosystem.” Two additional schedules are prioritized for “all major rivers and streams outside the Sacramento River watershed.” This report identifies 138 rivers and streams for instream flow studies. The total estimated cost to conduct scientific instream flow studies for the high priority rivers and streams tributary to the Delta is $32.46 million. The total estimated cost to conduct scientific instream flow studies for the high priority rivers and streams outside the Delta watershed is $107.25 million. The detailed schedules and costs are preceded with a few short discussions on the timelines given in the directive, the organization of schedules, the cost estimates for instream flow studies, and cost estimates for the next logical step: setting instream flow objectives.