Possible Clues:

• City on the Mexican border
• Texas city seen in many westerns
• U.S. city that hosts the world's largest jalapeño festival
• Texas City on the Rio Grande
• Northern end of the Gateway to the Americas International Bridge
• Texas city that hosts an annual jalapeno festival
• "The Gateway City" of Texas
• Southern terminus of I-35
• City in old westerns
• 60's series set in post-Civil War