Technical Talk Abstract:

Pleistocene Channels in the Central Valley of California: Potential Contaminant Pathways, and Exploitation for Groundwater and Minerals (Gold, Aggregates)

Roy J. Shlemon, Ph.D.

Independent Consulting Hydrologist

rshlemon@jps.net

Major rivers in the California Central Valley are underlain by multiple gravel-filled buried channels produced by regional climatic change (mainly Sierra Nevada glaciations). Buried lower American and Mokelumne river channels form the base of a sequence stratigraphy traceable to ~35 m below sea level. The Mokelumne River channels are specifically tracked to glacio-eustatically lowered base levels in the eastern California Delta. The channels are apparently progressively vertically offset by inferred latest Pleistocene to Holocene faults, which should therefore be regarded as “active” according to present California definition. They are typically expressed on the surface by relict paleosols (pedogenic) on inset terraces; downstream they are identified in water-well logs as the base of a grossly fining-upward sequence stratigraphy. Based on stratigraphic position, the older channels are inferentially at least ~600 ka old. An even earlier south-flowing American River channel “(early Fair Oaks age)” may be ~750 ka based on association with the Brunhes-Matuyama boundary. This channel may have flowed into an ancestral Tulare Lake (Corcoran Clay) prior to its inferred “catastrophic” drainage through the Carquinez Straits and into San Francisco Bay.  

Buried channels in the northern Sacramento Valley and the southern San Joaquin Valley similarly reflect Pleistocene climatic change, but their depths and downstream trends are largely controlled by local regional subsidence, particularly in the Tulare Basin. Historically, many Pleistocene channels were exploited for gold mostly by dredging and hydraulic mining. The buried channels are also important aquifers for domestic and agricultural water. Where expressed as terraces, the channels have long supplied sand and gravel for aggregate, an increasing valuable commodity for urban development. But the buried channels are also potential pathways for contaminants moving into the subsurface where downstream migration is not readily predictable owing to complex hydraulic connection via local fracture and fault systems. 

Dr. Roy J. Shlemon has been a consulting geologist for the past ~65 years. He resides in Newport Beach, and focuses mainly on application of geomorphology, Quaternary geology and soil stratigraphy to engineering practice. Dr. Shlemon received his doctorate from the University of California at Berkeley and was on the faculty of the University of California at Davis and the Louisiana State University in Baton Rouge. He has also lectured and given short courses at Stanford, UCLA and various California State Universities. Dr. Shlemon is also an active member of many academic and professional organizations including the Association of Engineering Geologists.  His specialty practice has taken him around the world as a consultant and technical advisor for geoarchaeological investigations, for fault-activity and mass-movement assessments, for related engineering-geological applications for construction of large dams, nuclear power and related waste facilities, and for residential and commercial developments. He has also serves as a technical consultant and expert witness for legal entities; and as a Technical Reviewer/Advisor for federal and local government agencies and international publishing firms.   In addition to his consulting practice, Dr. Shlemon holds appointments as Senior Fellow in the College of Letters and Science, and Research Associate in the Department of Earth and Planetary Sciences at the University of California, Davis.