CGS Geologic Hazard Notice — Smectitic Sediments

In 2009, the California Geological Survey issued a Geologic Hazard Notice to warn engineering and building departments in affected cities and counties over concern of problematic smectitic fluvial sediments occurring in the Sierra Nevada foothills of Central California and adjacent fringe areas of the Sacramento and San Joaquin Valleys.  The Geohazard Notice was warranted based on preliminary data and on-going investigations that show the potential for serious engineering problems associated with a little known Early Tertiary sedimentary unit that includes both landsliding and expansive soil behavior leading to severe foundation distress.

The latter issue has been an on-going problem for certain zones in a residential development in Eastern Sacramento County as well as elsewhere in Placer County.  (see GSA poster presentation).  The landslide issue is particularly of concern in Sierra foothill regions.  For example, reoccurring slope instability in the vicinity of Alta, Placer County has been recorded over the last 150 years.  This location is a transportation corridor with the convergence of railroad, interstate highway and local roadways.  Historically, all have been affected at one time or another and conditions favor future landslide occurrence here (see GSA poster presentation).  Landsliding associated with this sedimentary unit is pervasive throughout Nevada County and other areas to the north as well.

To view the CGS Geohazard Noitice for Smectite Sediments …click here

More up to date information can be obtained from Tim McCrink at the California Geological Survey

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