The United States shares over 1,900 miles of border with Mexico, with Arizona and South Texas sharing 387 and 697 miles of that border respectively. The border with Mexico and these two states includes different types of terrain that represent a significant challenge to border security efforts. For example, in Arizona, the border is characterized by desert and rugged mountains, while in South Texas, the border is divided by the Rio Grande. Threats along the southwest border include illegal entrants and the smuggling of drugs, firearms, and currency by criminal networks. According to U.S. Customs and Border Protection (CBP), corridors in Arizona and South Texas represent some of the highest-threat areas along the southwest border for illegal entrants and smuggling.