What makes all the food possible is irrigation -- water brought in from far away, a large part of it from snow pack in the mountains, and distributed throughout the Valley by a vast system of irrigation canals and pipes.
Our ABC News team drove three hours up into the Sierras to Sequoia National Park to see the fast-disappearing snow pack under the towering ancient trees.
Even though the Sierras had a snowfall far above average this past winter, as did many of the western mountain regions, in most places that didn't help the valleys much because the snowpack melted weeks too soon as it has been doing for some years with global temperature rising. And snowpack provides about three-fourths of the West's water.
The trouble is, as scientists studying the change explain, water normally used to trickle out over the summer. Now, running downhill too soon, it is leaving many valleys dry by midsummer, and crops withering.
San Joaquin farmers like Dan Errotabere, whose family corporation farms thousands of acres in the San Joaquin Valley, will get through this summer. But they must strain to use every drop.
Errotabere, like most working the rich ground, metes out water to his almond trees through pressurized tanks and lines.
The water distribution station next to his almond groves looks more like what you'd expect to find in a high-tech chemical factory -- shiny, round metal flasks, three feet in diameter, sealed tight against sun and drippage, interconnected by varying sizes of pipes and supports.
"It's all contained," Errotabere said, "so the only place that water should leak out is at the drip system."
For the farmers, it's as precious as oil. We found water meters spinning at the corners of fields all over the great valley. Like oil, it's expensive.
"Water is a big piece of our farm budget" he said.
And if water becomes even more scarce, thus more costly?
"Food prices will go up," he said matter of factly.
This summer, San Joaquin growers will probably have enough water. The dams and reservoirs built around the edges of California's Great Central Valley have just enough capacity to hold one year's supply.
But computer model projections shown to ABC News by eminent climatologist Steve Schneider at Stanford University, and other calculations from California state water boards, now warn that because of global warming the mountain snowpack so essential to all the food is most likely to be not only melting out too fast in the spring, but diminishing drastically -- by as much as 90 percent, according to some computer models -- before the end of the century, well within the lifetime of today's kids.
San Joaquin farmers are famous for their adaptability and ingenuity. They have to be to wring so much for America's tables from ground that naturally gets only eight inches of rain a year, and that only in winter.
And there's the pride and responsibility they feel as producers of nearly half our fruit and vegetables.
If anyone can figure out how to deal with hard times down on the farm, supplying the bursting supermarkets in which most American kids think the food they love so much somehow just magically appears, the San Joaquin farmers can.
But even San Joaquin farmers will need the water.