SH 20 begins where NM 460 (Co-signed with NM 478), also called Anthony Dr., reaches the state line between Anthony, New Mexico and Anthony, Texas in the El Paso area's Upper Valley. The route proceeds south through Anthony along Main St. passing Federal Correctional Institution, La Tuna. The route then enters Vinton where it becomes Doniphan Dr. Further south in Canutillo the route intersects Loop 375, El Paso's beltway. After entering the city of El Paso, the route intersects SH 178 which connects the route via NM 136 to the international border with Mexico south of Santa Teresa, New Mexico. Further south, SH 20 turns off of Doniphan Dr. and onto Mesa St. and soon after crosses the I-10 freeway which also carries US 85 and US 180 at this point. The route continues to the southeast passing through the foothills of the Franklin Mountains. The route then passes the University of Texas at El Paso and Sun Bowl Stadium before entering central El Paso.