N.M. Stat. § 67-5-8
If any proposed highway be on the county line between two counties, the board of county commissioners of each county interested shall be petitioned, and each of such boards shall appoint three viewers, qualified as in other cases, who, or a majority of whom, shall meet at a time and place named by the board of county commissioners first interested and proceed to view and mark out the road, and report to the board of county commissioners of both counties, as in other cases, and the concurrence of the county commissioners of both such counties shall be necessary to establish it. And, if any such road be established, each of such counties shall open and maintain a definite part thereof, which the board of county commissioners of such counties shall apportion by mutual agreement between the two counties, and if the board of county commissioners cannot agree upon their apportionment, they may refer the matter to three disinterested freeholders as arbitrators, whose duty it shall be to apportion the same and report thereon to the boards of county commissioners of both counties.
NMS § 67-5-8