Plotting several curves can allow the archaeologist to develop a relative chronology for an entire site or group of sites.
In 1929, they found a charred log near Show Low, Arizona, that connected the two patterns.
It was now possible to assign a calendar date to archaeological sites in the American southwest for over 1000 years.
In 1901, Douglass began investigating tree ring growth as an indicator of solar cycles.
Douglass believed that solar flares affected climate, and hence the amount of growth a tree might gain in a given year.
Secondly, annual rainfall is a regional climatic event, and so tree ring dates for the southwest are of no use in other regions of the world.
It is certainly no exaggeration to call the invention of radiocarbon dating a revolution.
Clark Wissler, an anthropologist researching Native American groups in the Southwest, recognized the potential for such dating, and brought Douglass subfossil wood from puebloan ruins.
Unfortunately, the wood from the pueblos did not fit into Douglass's record, and over the next 12 years, they searched in vain for a connecting ring pattern, building a second prehistoric sequence of 585 years.
Each tree then, contains a record of rainfall for the length of its life, expressed in density, trace element content, stable isotope composition, and intra-annual growth ring width.