Cahokia was once a city of 20,000 which was located where Collinsville, Illinois is now, just outside St. Louis. It is one of a small number of World Heritage sites in the United States. It was built by a mound-building culture, and flourished for a few hundred years about a thousand years ago.
We to Cahokia a few weeks ago while attending Nasfic. From our Collinsville hotel room, I looked at where we'd been on Google Earth and made an interesting discovery: the ghost of mound #31 lurks in the elevation data: An auction liquidation house now stands where mound #31 once stood. The elevation data shows the shape of the mound, whereas the aerial photo used by Google Earth shows the business that replaced it. (Download the_ghost_of_cahokias_mound_30..kmz)
Mound 31 was torn down in the 1960s as part of an expansion back when the building was a store called Grampa's. The main building was built in the 1940s as a nightclub. Mound 30 was torn down for the initial construction. GE probably uses the elevation data from the 1960s because it is 1 meter resolution. I'm guessing that this hi-rez elevation data dates from when the nearby interstate, which runs through the Cahokia archaeological site, was being constructed.
I looked into whether is was possible to do time-series digital archeology on sites like this, but the 1 meter resolution elevation data seems to have been a one-time thing, for Cahokia at least.
Our photos from Cahokia are HERE.