Every summer, they seem to magically appear — giant piles of fine powder that weigh four tons each. And then, they're gone.

The piles are a common site in the Sacramento region — from Highway 99 and the Garden Highway in Sutter County to Yuba, Stanislaus and Merced counties. 

It turns out, the white powder piles are mainstays in orchards.

Shane Broughton is an equipment operator for Sierra Gold Nurseries in Yuba City. 

"This stuff is gypsum," says Broughton. "It's a soil retardant and it loosens up hard soil and takes out the hard minerals and loosens those up inside of the soil so that it's easier to break down and you have a softer ground to plant your orchards in." 

Broughton explains why that's important.

"Roots don't grow so well in hard soil or compacted soil with big dirt clods in it," he says. "They tend to grow around those and your trees get a little wild. They don't stay in place in the ground as well if you don't have the softer soil."

Gypsum for farming purposes can be mined, manufactured or recycled by using old drywall that has been ground into a powder. The cost depends on the quality and can range from $20 per ton to $200 per ton.  Bob Moffitt / Capital Public Radio

There are also different types of gypsum and all are valuable for their sulphur content.

One type of gypsum is made using sulphur dioxide. It's one of the by-products of coal-fire burning. The sulphur dioxide is pumped through a slurry of lime powder and water before it all dries.

That type of gypsum costs about $40 per ton, but Broughton says it's better suited to make drywall.

The nursery buys its all-natural gypsum for $100 per ton from a mine in Nevada.

Broughton says it will take a couple of days to spread the material. Then he'll water it, till it, make rows and plant an orchard.