ON A SUNBAKED AUGUST MORNING, off a rural road in the heart of California’s Central Valley, a low-slung tractor rumbles between neat rows of identical, light-green trees. To its right, a plume of dust billows up, thick enough to blot out the sky above the treetops. A chute on the truck sends a steady stream of almonds flying into the trailer hitched behind.

Sweating as I skitter around to avoid the moving tractor, I’m witnessing what has emerged as one of the Central Valley’s most lucrative rituals: the almond harvest. Here in western Fresno County, which generates more than a fifth of California’s almonds, production has more than doubled since 2005. Almonds are now nearly as valuable as the state’s vaunted grape harvest.

Another truck has already been through the orchard, armed with a giant metal forceps that grabs each tree trunk and shakes it violently for a few seconds, sending nuts clattering to the ground like a slow-moving hailstorm. Next, sweepers come through, mounding the almonds into long, narrow piles along the center of each row. Last comes the harvester to hoover them up.

The pale, sandy soil is bone-dry — hence all the dust. But that has nothing to do with the drought that is gripping California, the region’s worst in decades. The San Joaquin Valley, which forms the southern half of the 450-mile-long Central Valley, is technically a desert: In good years, it relies on irrigation water guided in from mountain ranges to the north and east through an impressive system of channels. And in the weeks before a harvest, almond farmers cut way back on watering, both to hasten the ripening of the nuts and to ensure a dry bed for them when they fall. The harvest is a notoriously hot, dusty affair.

Charts and maps by Julia Lurie and Lei Wang

As I gape at the efficiency on display — just a few workers and machines can harvest thousands of trees in several hours — an angry voice cuts through the truck’s roar. “Hey!” It’s a guy who looks to be in his 20s, slender, in a dusty baseball cap, a plaid shirt, and jeans. He says he’s heard from my travel companions — a photographer and an almond specialist from the University of California Cooperative Extension named Gurreet Brar — that I’m a magazine writer looking into California’s almond boom. He demands to know what my angle is. Am I going to blame almonds for the state’s mounting water woes, like other articles have?

When I assure him I’m after the whole story, he softens. He declines to give his name or be interviewed at length, but says his family farms almonds, apricots, and raisin grapes. Now they’re pulling the grapes to put in more almonds — raisins, he explains, aren’t a very well-marketed crop, so it’s harder to make a profit. And with that, he excuses himself to go manage the harvest.