What flatlands circle the northern and western coastline of the gulf of mexico?

The flatlands of the 'Gulf Coastal Plain' circle the 'northern and western coastline' of the Gulf of Mexico.

Explanation:

The Gulf of Mexico is clearly circled by the coasts of US and Mexico on its closed side. In both countries, this continued coastal line circling the gulf and the adjacent region that stretch a little deeper into the interiors of both the countries are collectively called the 'Gulf Coastal Plain'. It comprises of the coasts of eastern and the upper-southern Mexico, southeastern Texas, western Florida, and southern Louisiana. The region is called so owing to the absence of any naturally occurring geographical features of varied elevation.

The Gulf of Coastal Plain, also known as the Oil Coast. It extends around the Gulf of Mexico in the Southern United states and Eastern Mexico.