One fact I find notable with these "massive" societies in the American South West is how small they were. For example, the linked article describes a site with

One fact I find notable with these "massive" societies in the American South West is how small they were. For example, the linked article describes a site with hundreds of rooms. That implies thousands of people. And, Chaco was the kingpin. Many other fascinating sites, such as Walnut Canyon, had "tens of rooms."