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U.S. Geological Survey Open-File Report 2011–1262

Location and Age of Foraminifer Samples Examined by Chevron Petroleum Company Paleontologists from More Than 2,500 Oil Test Wells in California

By Earl E. Brabb

Thumbnail of and link to report PDF (1 MB)Introduction and Background

Chevron Petroleum Company in 2001 donated an estimated 50,000 foraminifer slides, 5,000 well logs, geologic and surface locality maps, and paleontologic reports to the California Academy of Sciences and Stanford University for safekeeping, because they stopped or cut back exploration for petroleum deposits in California. The material was loaned to Earl Brabb temporarily so that information useful to the U.S. Geological Survey could be extracted. Among the estimated 5,000 well logs, more than 2,500 were printed on fragile Ozalid paper that had deteriorated by turning brown and hardening so that they could be easily damaged. These 2,516 well logs were scanned to provide a digital copy of the information (data set 1, posted separately at

The 2,516 wells extend over an area from Eureka in Humboldt County south to the Imperial Valley and from the Pacific Ocean east to the eastern side of the Great Valley and the Los Angeles Basin. The wells are located in 410 7.5-minute quadrangle maps in 42 counties. The digital information herein preserves the data, makes the logs easily distributed to others interested in subsurface geology, and makes previously proprietary information widely available to the public for the first time.


  • Report PDF—explanatory text for this publication (1 MB)
  • Data

  • Readme TXT—File that explains the data sets (4 kB)
  • Data Set 1 folder—Scanned images of the original logs for each of the 2,516 wells (5.7 GB total)
  • Data Set 2 folder—Well location and summary for each of the 2,516 paleologs (spreadsheet in several formats; 5.2 MB total)
  • This report is available only on the Web.

For additional information:
Contact Information, Western Region Geology and Geophysics Science Center—Menlo Park
U.S. Geological Survey
345 Middlefield Road, MS-973
Menlo Park, CA 94025-3591

Part of this report is presented in Portable Document Format (PDF); the latest version of Adobe Reader or similar software is required to view it. Download the latest version of Adobe Reader, free of charge.

Suggested citation:

Brabb, E.E., 2011, Location and age of foraminifer samples examined by Chevron Petroleum Company paleontologists from more than 2,500 oil test wells in California: U.S. Geological Survey Open-File Report, 2011-1262, 4 p. and data files, available at


Introduction and Background

Information Provided

Ages of Foraminifers


References Cited

Readme file

Data Sets

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