The skinny rings of ancient giant sequoias and foxtail pines hold a lesson that Californians are learning once again this winter: It can get very dry, sometimes for a single parched year, sometimes for withering decades.
Drought has settled over the state like a dusty blanket, leaving much of the landscape a dreary brown. Receding reservoirs have exposed the ruins of long-forgotten towns. Some cities are rationing supplies and banning outdoor watering. Many growers are expecting no irrigation deliveries from the big government water projects that turned the state's belly into the nation's produce market.
Recent storms in Northern California and forecasts of more to come in the next week or two have lessened fears that this drought will break records as the worst in modern times. But it is unlikely to end soon, highlighting the vulnerability of the state's water supply.
Even when nature behaves, there are too many water demands for them all to be satisfied.
"California is running out of options to deal with the fact that it has basically been relying on more water than it has long-term access to," warned David Hayes, a former U.S. Interior Department official who was the Obama administration's point man on Western water issues during the president's first term.
"It's like reality is closing in on California," Hayes said.
A decade ago the state agreed to stop using more than its share of Colorado River water, cutting an important Southland supply. So much water is diverted from the watersheds of the state's two largest rivers, the Sacramento and San Joaquin, that their common delta is on the brink of ecological collapse, triggering environmental restrictions on delta exports.
Agriculture chronically pumps more water out of Central Valley aquifers than man or nature puts back. During droughts like this, growers suck up even more groundwater, compounding the problem. The state's acreage of almond and other nut and vine crops has ballooned, hardening the demand for irrigation supplies during dry spells.
A warming climate is shrinking the Sierra Nevada snowpack that acts as a natural reservoir. And although it is unclear exactly how climate change will affect precipitation levels in California, rising temperatures mean farm fields and suburban yards will dry out more quickly.
"I think that any prudent — fill in the blank — businessperson, governmental official, citizen, farmer would be thinking about how they can use less water" in the future, Hayes said.
Then there is California's annual rain and snowfall, which go up and down like a yo-yo.
"From a climate perspective, we've been here before," Martin Hoerling, a federal research meteorologist, said last week at a drought forum in Sacramento. "We shouldn't be surprised."
The state dried out like a prune in 1976-77 and before that in 1924, the most parched periods in the modern record. And ancient tree-ring records show that during the last millennium, conditions have at times been even worse.
Take the year 1580, which left the narrowest growth ring — or none at all — in the California trees that University of Arizona scientist David Meko used to reconstruct a 1,000-year history of stream flow in the Sacramento River Basin, the source of much of the state's water supply.
"You see things like 1580 — hey, this can happen," said Meko, who also detected periods of low river flow that lasted decades.
"We've given away more than nature provides," said Peter Gleick, an internationally recognized water expert and president of the Pacific Institute, an Oakland-based think tank.
"I think the current drought opens the door to a real conversation about fundamental changes in California water policy," Gleick said.
He ticked off what he considers the state's spendthrift water ways: California still has too many inefficient dishwashers, toilets and washing machines. Roughly 40% of the state's farmland uses wasteful flood irrigation, in which water flows by gravity down open ditches or across fields.
The state also has too many thirsty lawns, he said. Water for most people is too cheap. Most troubling to Gleick and many other experts: California doesn't regulate the use of groundwater, putting it at odds with most other Western states.