California's soil is extremely parched. Its ground is cracking, its rivers and lakes are low, it valleys are shrinking, and its mountains are rising. The state's drought has persisted for nearly two years. Now, researchers say the severity of the situation is unprecedented in modern times -- the worst drought in 1,200 years.

In a recent study, researchers from the Woods Hole Oceanographic Institution and the University of Minnesota compared California's current condition to precipitation data ascertained from the tree rings of blue oak trunks.

"California's old blue oaks are as close to nature's rain gauges as we get," study author Daniel Griffin, a geography professor at Minnesota, said in a press release. "They thrive in some of the driest environments where trees can grow in California."

The blue oak data allowed scientists to create a timeline of rainfall patterns dating back to the 13th century. While historically, the last two years of low precipitation isn't unprecedented (periodic dry spells are relatively common in California), Griffin and his colleagues say the combination of little rain and exceptionally high temperatures suggest the state's current drought is the worst in 1,200 years. Water levels, researchers say, haven't been this depleted in over a millennium.

"While it is precipitation that sets the rhythm of California drought, temperature weighs in on the pitch," WHOI paleoclimatologist Kevin Anchukaitis said.

While recent rains -- and a predicted wetter-than-normal winter -- may help some parts of California emerge from the current drought, researchers say climate models suggest the last two years are to some extent emblematic of a new normal.

"There is no doubt," Anchukaitis said, "that we are entering a new era where human-wrought changes to the climate system will become important for determining the severity of droughts and their consequences for coupled human and natural systems."

The work of Anchukaitis and Griffin was detailed this week in the latest issue of Geophysical Research Letters.