Yeah the wild thing about the southwest is the open-air museum aspect of it, not the layers on layers. For petroglyphs, the southwest has so many that date to the high middles ages (~1100 AD) you can stumble on them by accident as a hiker. AFAIK the oldest in the area are still thought to be these ones[0], about 9000 years ago. (Always controversial to date rocks I guess, but the oldest North American mummy should be easier and is about the same.[1])

[0] https://en.wikipedia.org/wiki/Winnemucca_Lake [1] https://en.wikipedia.org/wiki/Spirit_Cave_mummy#Dating

The southwest has plenty of layers on layers. Tucson is built on a Spanish fort, which is built on native villages on top of yet older native villages going back almost 4,000 years, as one example.

For another example, most neighborhoods in eastern phoenix are built on top of old Hohokam villages, adjoining older basketmaker sites. The canals throughout the city often follow the old Hohokam canals. Fun fact, the Intel Chandler campus is on top of old hohokam suburbs of Pueblo de los muertos, which is buried under the modern suburbs.

The Puebloan culture in the southwest during that time was basically a full fledged civilization. It's insane how underresearched such a culture is despite having built megastructures like within the Grand Chaco Canyon