Hoover in China: Yet Another Note
Signs of the Impending Apocalypse:

Places You Must See: Mesa Verde

Mesa Verde, Colorado. Population ca. 1270, ca. 5000. Population of the Four Corners in ca. 1270 ca. 45000--more than today. Perhaps 500 people slept in this, with a natural roof, steady seep-springs of water, and lots of defensive protection. Their corn-beans-squash farms were on the mesa proper above.

By 1300 they were all gone...

Mesa Verde National Park: http://www.nps.gov/meve/