[jjotto]

...like most Precolumbian sites, it consisted of, well, a freakin’ mound of dirt...

Yep. Usually they contain bones and surprisingly few artifacts, so unless they are unusually large, they are forgotten or of only local interest.

[SunkenCiv]

The most interesting thing about these mound-builder sites is that they generally (not always) turn out to be part of a layout that resembles cities in the pyramid-building civs of Central America and Mexico.