YOU ARE LEGALLY REQUIRED TO CONTRIBUTE. California law requires each owner to share the cost of maintaining the road. Here is California Civil Code section 845:
(b) If the easement is owned by more than one person, or is attached to parcels of land under different ownership, the cost of maintaining it in repair shall be shared by each owner of the easement or the owners of the parcels of land, as the case may be, pursuant to the terms of any agreement entered into by the parties for that purpose. In the absence of an agreement, the cost shall be shared proportionately to the use made of the easement by each owner. (c) If any owner refuses to perform, or fails after demand in writing to pay the owner’s proportion of the cost, an action to recover that owner’s share of the cost, or for specific performance or contribution, may be brought by the other owners, either jointly or severally. The action may be brought before, during, or after performance of the maintenance work