The U.S. southern border is formed by Mexico and the Gulf of Mexico.
The gulf that forms part of the southern border of the United States is the Gulf of Mexico
Southern Alabama touches the Gulf of Mexico. Alabama's beach vacation areas on the Gulf of Mexico include Gulf Shores and Orange Beach.
Rio grande
The river which forms part of the border between the Rocky Mountains and the Pacific Ocean is the Columbia River.
Florida
The Rio Grande
Florida.
columbia river
The Gulf of Mexico
Rio grande
Rio grande