Yes, Spanish Fort sits atop their landfill.
To archaeologists like Ryan Gray, of the University of New Orleans, the midden is “so much more than a dump.” That’s because in academic terms, the Marksville people who built it are referred to as an “archeological culture,” meaning all that is known about them comes from the artifacts and structures they left behind — structures like the shell mound under Spanish Fort and the items deposited within.
With that term, Gray said, “We're just talking about a shared way of doing things that results in some broad similarities in material culture. But within that, there can be considerable variation, and there may be little evidence that the people of what we call an archaeological culture thought of themselves as a unified group.
"Archaeological cultures become ways that we try to make sense of variation in material culture (manifested as pottery styles, house types, ways of subsisting, spiritual beliefs), but we try not to give it an agency so it doesn't become confused with the peoples who are part of it."