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....

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.

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.