LOS ANGELES — Ever since the Gold Rush, California farmers have staked their claim to water and ferociously protected their rights to use it to irrigate the crops that have made the state the greengrocer for the nation.

But on Friday, in a sign of how the record-setting drought is shaking up established ways here, state officials accepted an offer from farmers in the Sacramento-San Joaquin River Delta to give up a quarter of their water this season, either by leaving part of their land unplanted or finding other ways to reduce their water use. In return, the state has assured them that it will not seek further reductions for the growing season.

The deal is an important concession from a relatively small number of growers that officials hope will prompt similar agreements throughout the state’s agricultural industry, which uses 80 percent of the water consumed in the state in a normal year.

“We’re in an unprecedented drought, and we have to exercise the state’s water rights in an unprecedented way,” said Felicia Marcus, the chairwoman of the State Water Resources Control Board. “This is a breakthrough in what has long been a rhetorical battle. It’s a significant turning point to have people say, ‘We know this is complicated. We want to do something early in good faith that is a pragmatic solution for everyone.’ ”