Global (i.e., eustatic) sea level change, as has frequently occurred (with relative levels perhaps as high as +40 m and as low as -130 m) during the last 2 million years, drives a landward migration of the coastline during times of rising sea level and the reverse when sea level falls. To this simple scenario, in the northeastern Gulf of Mexico (Mississippi-Alabama-West Florida), the complicating factor of irregular uplifting, subsidence, and possible faulting by ongoing processes driven from Earth's interior (that is, neotectonics) occurring along with the sea level change must also be considered.