CORCORAN, Calif. — The waters from a long-dry lake, resurrected by epic rains earlier this year, already lap at the levee of this Central Valley town of 22,000 people. A hundred square miles of crops are drowning around it. But the flood that Corcoran City Manager Greg Gatzka is really worried about has yet to come.

That flood — frozen in a historic snowpack — is still sleeping, piled around Sequoia trunks, some 80 miles away. Unseasonably warm temperatures are starting to wake it up.

For Gatzka, warmer temperatures mean "the snowpack, the ominous thing that we can see on the horizon ... is coming our way," he said.

Four major rivers empty into the landlocked southern end of the Central Valley and the clay-packed bed of the Tulare Lake Basin. All start in the snow-packed Sierra Nevada mountains and end, eventually, in the fast-growing expanse of Tulare Lake — what used to be the largest freshwater lake west of the Mississippi River.