Here's a good site about the Western Pond turtle (Pacific Pond turtle) in California, and includes its status as a "species of special concern".

http://www.dfg.ca.gov/hcpb/cgi-bin/more_info.asp?idKey=ssc_tespp&specy=reptiles&query=Clemmys%20marmorata

It appears as if no wildlife can legally be taken from the wild unless there is a special provision in the law or allowed by permit.

http://www.leginfo.ca.gov/cgi-bin/displaycode?section=fgc&group=01001-02000&file=2000-2019

Here's the California Fish and Game Code...good luck with that.

http://www.leginfo.ca.gov/cgi-bin/calawquery?codesection=fgc&codebody=&hits=20

You can probably find the information you need from a 10 minute telephone call to (916) 653-4875. Good luck.