Cal. Bus. & Prof. Code § 7839.2
(a) A professional geologist or professional geophysicist shall use a written contract when contracting to provide geological or geophysical services to a client pursuant to this chapter. The written contract shall be executed by the professional geologist or professional geophysicist and the client or the client’s representative prior to the professional geologist or professional geophysicist commencing work, unless the client states in writing that work may be commenced before the contract is executed. The written contract shall include, but is not limited to, all of the following:
(b) Subdivision (a) shall not apply to any of the following:
(4) Geological or geophysical services rendered by a geologist or geophysicist to any of the following: