Hi,
   I have not billed to Medi-Cal Before.  Is that the California Medicaid?  If Medicare is prime, you definitely need to file with them first.  After you receive the eob you would file the Medi-Cal.  Our NY Medicaid requires special forms to be completed.  When they are 2ndary you indicate the primary payment right on the form and you do not attach a copy of the EOB.
Good Luck
Michele