There Is No Gulf Coastal Plain in Mexico

The Gulf Coastal Plain is a U.S. physiographic province extending along the northern Gulf of Mexico—from the Florida Panhandle west through Alabama, Mississippi, Louisiana, and into Texas.

Mexico has its own Gulf-facing coastal plains (Tamaulipas, Veracruz, Tabasco, Campeche, Yucatán), but they are distinct geological provinces—part of the Gulf of Mexico Coastal Plain (Mexican sector) or the Yucatán Platform—not the U.S.-defined "Gulf Coastal Plain."

Mexican Gulf Coast Regions

• North Mexican Gulf Coastal Plain: Tamaulipas, N. Veracruz — alluvial, deltaic, petroleum-rich
• South Mexican Gulf Coastal Plain: S. Veracruz, Tabasco — tropical, wetlands, oil/gas
• Yucatán Peninsula: Limestone platform, cenotes, distinct karst geology

So while Mexico has Gulf coast lowlands, the term "Gulf Coastal Plain" specifically denotes the U.S. geographic region.