http://www.leginfo.ca.gov/cgi-bin/displaycode?section=prob&group=15001-16000&file=15200-15212
"15200. Subject to other provisions of this chapter, a trust may be
created by any of the following methods:
(a) A declaration by the owner of property that the owner holds
the property as trustee.
(b) A transfer of property by the owner during the owner's
lifetime to another person as trustee.
(c) A transfer of property by the owner, by will or by other
instrument taking effect upon the death of the owner, to another
person as trustee.
(d) An exercise of a power of appointment to another person as
trustee.
(e) An enforceable promise to create a trust."
I dont know but i would think it may be very difficult to successfully contest a trust based on lack of witnesses alone.