Authorities in California are trying to crack the case of a nut thief who made off with 140,000 pounds of walnuts.

The theft, estimated at nearly $400,000, occurred in the small Central Valley town of Escalon. Investigators say it was one of the biggest to hit the booming industry. In October, about 12,000 pounds of walnuts worth $50,000 were stolen from a trailer parked on Highway 99 north of Sacramento.

This time several truckloads of walnuts were taken from the facility. Authorities say rising prices — about $2 per pound — is what appears to be driving the recent walnut thefts.

No arrests have yet been made.

Walnuts are California’s fourth-leading agricultural export. China remains the world’s leading producer of walnuts.