The Great Drought was at least partially responsible for the migration of people away from southwestern Colorado in the late thirteenth century; archaeologists are still examining the social, political, religious, and environmental implications of this important event in pre-Columbian history.
The Gault archaeological site is an extensive, multicomponent site located in central Texas, United States, about 40 miles north of Austin.
The behavioral aspect of tree-ring dating, meanwhile, allows archaeologists to understand ancient wood-use practices, trade, and other activities.
Tree-ring dating may only be performed on tree species that produce one growth ring per year, and do so in response to annual variations in precipitation (and in some cases temperature).
Cross-dating is accomplished by documenting, analyzing, and matching repeated patterns of wide and narrow rings in tree-ring cores collected first from the same tree, then from trees in the same stand, and then from sites in the same region, all of which are responding to variations in the same climatic variable (e.g. Then, by working backward from the current year, the dendrochronologist is able to determine the exact year in which each growth ring was formed, thus producing a master tree-ring chronology.
Ring patterns from newly collected specimens, such as those from archaeological sites, are then compared to the master chronology in order to provide a tree-ring date for that specimen. First, tree-ring dating is about matching patterns, not counting rings.
These large datasets allow archaeologists to understand the occupation and abandonment of southwestern Colorado with unprecedented precision.
In another major contribution to science, Douglass used tree rings to infer that a “Great Drought” had occurred across the American Southwest from AD 1276 until 1299.
The temporal aspect of tree-ring dating has the longest history and is the most commonly known—tree rings can be used to date archaeological sites, such as the Cliff Dwellings found at Mesa Verde National Park (MVNP) or historic cabins.
In the 1930s archaeologist Earl Morris of the Carnegie Institution supplied Douglass with numerous wood specimens from Johnson Canyon, Colorado, south of MVNP, in an effort to extend his ability to date sites back to about 2,000 years ago.
Also in the 1930s, Zeke Flora, an amateur archaeologist based in Durango, sent wood and charcoal specimens to Douglass.
In the last several decades, with the location, investigation, and reporting of a growing number of sites with reliable dating, more and more American archaeologists now believe the western hemisphere was occupied at least several thousand years prior to the appearance of diagnostic Clovis materials.
Most of these sites are widely spaced geographically and do not contain an extensive array of associated lithic materials that would show a diagnostic pattern of tool production and use.
Everything else being equal, in a wet year trees will produce a larger growth ring.