California Unemployment Insurance Code Section 455.5

This state shall participate in any arrangements for the payment of compensation on the basis of combining an individual`s wages and employment covered under this division with his wages and employment covered under the unemployment compensation law of other states which are approved by the Secretary of Labor in consultation with the state unemployment compensation agencies as reasonably calculated to assure the prompt and full payment of compensation in such situations. Any such arrangement shall include provisions for both of the following: (a) Applying the base period of a single state law to a claim involving the combining of an individual`s wages and employment covered under two or more state laws. (b) Avoiding duplicate use of wages and employment by reason of such combining.