What is the southernmost US state that borders Mexico?

Texas is the southernmost US state that shares a border with Mexico. The boundary between Texas and Mexico stretches approximately 1,254 miles along the Rio Grande River. This extensive border allows Texas to have substantial interaction with Mexico culturally, economically, and geographically.

When considering the other options, while California, New Mexico, and Arizona also share borders with Mexico, they are located further north than Texas. California's border lies to the west of Texas, New Mexico is to the northwest, and Arizona is also north of Texas. Thus, while these states have important geographical and cultural connections to Mexico, none extend as far south as Texas, making it the correct answer to the question.