A study published in the journal of Quaternary Science Reviews in June of 2015 suggests that much of the deserts of the western U.S. were damp until about 8,200 years ago. According to earthsky.com, ancient shorelines line the hills and mountains above the dry valley floors in areas of Utah, Nevada, eastern California and southern Oregon. Even though most of the ice sheets of the last ice age retreated around 12,000 years ago, many of these areas still remained much wetter than today.
Researchers came to this conclusion by studying stalagmites, which are pillars of deposited cave dripping that form over hundreds of thousands of years as water seeps down into the ground and into caves. The layers of the stalagmites essentially record a region's moisture over time.
Photo Credit: Christine Y. Chen
The researchers looked at two stalagmites and compared their ages, and then analyzed the samples to determine the moisture content. The samples all ranged from 4,000 to 16,000 years old. What they found was that the moisture content seemed to drop dramatically in samples less than 8,200 years old.
Researcher David McGee, Assistant Professor in MIT's Department of Earth, Atmospheric and Planetary Sciences, said "Based upon these data, I would hypothesize that you should see some pretty big changes in how people were living just before and right after 8,000 ears ago. What sort of game were they hunting, what plants were they eating, and where were they choosing to live?"
Researchers are still working to determine what exactly caused this drying to occur over such a relatively short period of time.