Looking Back On Time an article by Claire Rogers in Desert Leaf

Because the Earth’s magnetic poles wander erratically over time, the magnetic orientation of artifacts from a site can be tied to specific dates in the geologic time scale.
Archaeologists love a good mystery, and they have found one at the base of the Tucson Mountains. One quarter mile from the West Branch of the Santa Cruz River, near what is now the intersection of Mission and Irvington roads, a complex of ancient settlements bears the markers of abrupt change. From A.D. 950 to 1140, agriculture in the area appeared to be on the rise and the population in flux. Initial archaeological research at the West Branch site began in 1984; nine years later, additional inquiry added volumes to what was previously known about the boom and bust of this period in Tucson’s pre-history.

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