By now, the impacts of California's unchecked groundwater pumping are well-known: the dropping water levels, dried-up wells and slowly sinking farmland in parts of the Central Valley.

But another consequence gets less attention, one measured not by acre-feet or gallons-per-minute but the long march of time.

As California farms and cities drill deeper for groundwater in an era of drought and climate change, they no longer are tapping reserves that percolated into the soil over recent centuries. They are pumping water that fell to Earth during a much wetter climatic regime—the ice age.

Such water is not just old. It's prehistoric. It is older than the earliest pyramids on the Nile, older than the world's oldest tree, the bristlecone pine. It was swirling down rivers and streams 15,000 to 20,000 years ago when humans were crossing the Bering Strait from Asia.
"What I see going on is a future disaster," says Vance Kennedy, a retired research hydrologist. "We are mining water that cannot be readily replaced."

Tapping such water is more than a scientific curiosity. It is one more sign that some parts of California are living beyond nature's means, with implications that could ripple into the next century and beyond as climate change turns the region warmer and robs moisture from the sky.

"What I see going on is a future disaster. You are removing water that's been there a long, long time. And it will probably take a long time to replace it. We are mining water that cannot be readily replaced," said Vance Kennedy, a 91-year-old retired research hydrologist in the Central Valley.

much more:

http://www.motherjones.com/environment/2015/03/california-pumping-water-fell-earth-20000-years-ago