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Paleontology of the Yuba River Test Hole: New Discoveries in Yuba County, CA
Reprised from 2007

Chris Bonds, PG, CHg

CA Department of Water Resources

 

PRESENTATION:

The California Department of Water Resources has been working cooperatively with the Yuba Water Agency (YWA), local water districts/companies, and private parties to monitor groundwater level and quality conditions in Yuba County since the 1990s. To supplement an existing network of agricultural, domestic, and observation wells used for groundwater monitoring purposes, a deep exploratory test hole (YR-1) was drilled, and a dedicated multi-level monitoring well was installed in June 2004 on the south side of the Yuba River, east of Marysville. What makes this groundwater monitoring site unique and particularly useful is that it is co-located next to an actively monitored streamgaging station operated and maintained by the YWA/USGS. The multi-level monitoring well continues to provide valuable data on the hydrogeologic conditions of Yuba’s groundwater subbasins; however, the geology and paleontology of exploratory test hole YR-1 are the primary focus of this talk. 

The exploratory test hole YR-1 penetrated Holocene through at least Eocene-age sediments and sedimentary rocks from the ground surface to a total exploration depth of 1,020 feet below ground surface (bgs). Geologic units penetrated include: Recent Alluvium, Riverbank Formation, Laguna Formation, Mehrten Formation, Neroly Formation, Upper Princeton Valley Fill, Ione Formation, and Capay Formation. Geophysical data indicates a zone of poor water quality is present below a depth of 624 feet bgs. Nested well completions were installed at depths of 70 to 80 feet bgs (YR-1A), 250 to 260 feet bgs (YR-1B), 430 to 450 feet bgs (YR-1C), and 600 to 620 feet bgs (YR-1D) across the Riverbank, Mehrten, and Neroly Formations, respectively.

Detailed evaluation of drill cuttings between 760 and 810 feet bgs has yielded significant new information on the fauna, age, and depositional environment of the Capay Formation in this area. To date, 140 fair to excellently preserved fossil specimens (1 to 6 mm in size) have been recovered including: 86 gastropods (snails), 21 scaphopods (tusk shells), 19 bivalves (clams), 13 solitary corals, and one shark tooth. Additionally, hundreds of other fair to poorly preserved fossil specimens and fragments were recovered between the depths of 760 and 860 feet bgs. Identification and correlation of several age-diagnostic index fossils indicates that this section of the Capay Formation was deposited between 46 and 50 million years ago. This correlates with the lower to middle Eocene Epoch and the “Domengine” and “Transition” Molluscan Stage ranges. Paleontology, lithology, and geophysical evidence suggest that the Capay Formation represents a shallow-marine shelf depositional environment under tropical conditions.

These paleontology findings are significant for many reasons, including:

  • This is the first reported discovery of Eocene-age fossils in Yuba County.
  • No significant Eocene fossil discoveries have been documented in northern California since the 1940’s.
  • Most of the fossils found are extremely small and probably represent juvenile or possibly dwarf/pygmy species.
  • The geographic range of some of the fossil species recovered has been extended into Yuba County.
  • Some of the fossils collected do not appear to have been found elsewhere which suggests that there may be some new species in this collection.

Work to finalize the fossil identifications and reporting is nearly complete. Future publishing of this discovery and associated geologic findings comprehensively in a peer-reviewed scientific journal will add an exciting new chapter to the Eocene paleontological and geological history of northern California.

SPEAKER BIO:

Chris Bonds is a Senior Engineering Geologist with the California Department of Water Resources (DWR) in Sacramento. Since 2001, he has been involved in a variety of statewide projects including exploration, monitoring, modeling, policy, research, and water transfers. Chris has over 28 years of professional experience in paleontology, geophysics, and environmental/engineering geology, within the private/public sectors, in California, Alaska, and Hawaii. He holds a master’s degree in Geology and is a Professional Geologist and Certified Hydrogeologist. Chris has been a member of GRA since 2010, a Sacramento Branch Officer since 2017, and has presented at various GRA events since 2004. He is a two-time co-recipient of GRA’s Kevin J. Neese Award for DWRs contributions to the Bulletin 118-03 - California’s Groundwater publication (2004) and for DWRs contributions to improving groundwater management and protection statewide (2015). Lastly, Chris co-authored a book titled Geology of Sacramento, California which was published by the Association of Environmental & Engineering Geologists in January 2021.

California Department of Water Resources, Division of Regional Assistance, Office of the Chief, 901 P Street, Sacramento, CA 95814; Phone (916) 657-1758; Email: chris.bonds@water.ca.gov

MEETING SPONSOR:

MEETING COSTS AND RSVP:

This meeting will be provided to members at no cost but registration is necessary to receive call-in information.

Member Price: FREE

Non-Member Price: $10.00

Student Price: FREE

CONTACT INFORMATION:

If you have any questions, please contact Michael Bombard at mbombard53@yahoo.com.

 



Date and Time

Tue, March 30, 2021

5 p.m. - 6:30 p.m.
(GMT-0700) US/Pacific

Location

Zoom



Zoom information will be sent after registration.

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