The Creek tribe don't want any more digging to occur (ancestors are buried there), so they purchased ground-penetrating radar.

...just beneath the plow zone atop that largest of Etowah's mounds, radar and other remote sensing instruments have revealed the foundations of three, perhaps four, previously unknown buildings — including one massive square structure 54 feet on a side — that appears to have been the ruler's residence. Because the mounds were built one hand-carried basket of earth at a time, they rose slowly from the surrounding river plain. As a result, the buildings atop the largest found — which sprawl across an acre of real estate — were probably constructed late in Etowah's history, probably between 1325 and 1375. "These structures are huge," says King. "This is clearly a much more complex place than we imagined."

Source: AJC.com