The Surface of Crystalline Basement, Great Valley and 
Sierra Nevada, California: a Digital Map Database

by 

Carl M. Wentworth, G. Reid Fisher, Paia Levine, and Robert 
C. Jachens


U.S. Geological Survey Open-File Report 95-96


1995


Crystalline basement in central California extends westward 
from the exposed Sierra Nevada beneath the sedimentary fill 
of the Great Valley and under the eastern edge of the Coast 
Ranges at mid- crustal depth (figure 1, and see ccb_fig1.ps 
or ccb_fig1.pdf). The surface of this basement is defined 
from three types of control: in the Sierra Nevada from the 
topography itself, beneath the eastern two thirds of the 
Great Valley in considerable detail from numerous wells 
drilled for oil and gas, and beneath the western San 
Joaquin Valley in less detail from seismic reflection and 
refraction profiles. Together, these data demonstrate that 
the surface of crystalline rock is continuous from the 
exposed rock in the mountains to the top of high-velocity 
rock buried deep beneath the eastern front of the southern 
Coast Ranges.

This report presents a compilation of data through 1985 
that define the surface of this crystalline basement, a 
contour map of the surface, and the lithology of the 
basement rock sampled by many of the wells. The compilation 
was begun as part of the investigation of the 1983 Coalinga 
earthquake (Wentworth and Zoback, 1990; Yerkes, Levine, and 
Wentworth, 1990), and was subsequently converted to digital 
form and extended to the whole of the Great Valley and 
Sierra Nevada. The main purpose was to explore and document 
the shape and continuity of the basement surface and to 
determine the relation of the surface to the tectonic wedge 
hypothesis (Wentworth and others, 1984; Wentworth and 
Zoback, 1989). Available basement samples from wells -- 
principally the thin-section collection of May and Hewitt 
(1948) preserved by the California Academy of Sciences -- 
were also reexamined by cooperating petrologists in an 
effort to distinguish wells that bottomed in ophiolitic 
rocks. 
 
 
CONTENTS OF REPORT

Processing of the compressed tar file (ccbsmt.zip) will 
yield a suite of files, including Arc export files, shape 
files, text files, and a page-sized map, involving several 
file formats, as follows:

     ccbsmt.text     - An ASCII file containing this text 
                       (without figure 1).
       ccbsmt.ps     - Postscript version of this text 
                       (without figure 1).
     ccbsmt.pdf      - pdf version of this text, including 
                       figure 1.
     ccb_fig1.ps     - the original (1995) Postscript 
                       version of the summary map (figure 
                       1).
     ccb_fig1.pdf    - A colored version of  figure 1 
                       prepared (2007) from ccb_fig1.ps.
     ccb_wells.ps    - Postscript tables of the basement 
                       and constraining wells. 
     ccb_wells.pdf   - Tables of the basement and 
                       constraining wells in pdf form.
     ccb_wells.asc   - An ASCII version of ccb_wells.ps. 
     lam2dd.prj      - projection file used to convert 
                       coverages in Lambert projection to
                       geographic coverages in decimal 
                       degrees, from which the shape files 
                       were prepared.
     import.aml      - An AML to convert the following 
                       export files to coverages in 
                       ARC/INFO. 

  Coverage export files (with coverage names assigned by 
  import.aml)
     ccb-bwells.e00  - export file for the basement 
                       wells (ccb-bwells).
     ccb- cont.e00   - export file for the basement 
                       contours (ccb- cont).
     ccb-cwells.e00  - export file for the constraining 
                       wells (ccb- cwells).
     ccb-qbndy.e00   - export file for the boundary of 
                       Quaternary alluvium in the Great 
                       Valley (ccb- qbndy).
     ccb-seis.e00    - export file for the seismic lines 
                       and elevation points (ccb- seis).

  Shape files      
     cb-bw           - files cb-bw.dbf, cb-bw.shp, 
                       cb-bw.shx (from  ccb-bwells)
     cb-cn           - files cb-cn.dbf, cb-cn.shp, 
                       cb-cn.shx (from  ccb-cont)
     cb-cw           - files cb-cw.dbf, cb-cw.shp, 
                       cb-cw.shx (from  ccb-cwells)
     cb-qb           - files cb-qb.dbf, cb-qb.shp, 
                       cb-qb.shx (from  ccb-qbndy)
     cb-sl           - files cb-sl.dbf, cb-sl.shp, 
                       cb-sl.shx (from  ccb-seis)