Cal. Civ. Proc. Code § 428.80

The counterclaim is abolished. Any cause of action that formerly was asserted by a counterclaim shall be asserted by a cross-complaint. Where any statute refers to asserting a cause of action as a counterclaim, such cause shall be asserted as a cross-complaint. The erroneous designation of a pleading as a counterclaim shall not affect its validity, but such pleading shall be deemed to be a cross-complaint.