O’NEALS, Madera County (AP) — Authorities in Central California say they have seized more than 500 full-grown marijuana plants from a sophisticated growing operation near Fresno.

Agents with the Madera County Narcotic Enforcement Team said they dismantled four greenhouses filled with plants during the pot best on Thursday in O’Neals, an unincorporated community 30 miles north of Fresno. No arrests have been made.

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Madera County Sheriff’s Office spokeswoman Erica Stuart says some of the greenhouses were nearly as large as football fields. Agents found another 100 starter plants that were ready to be put into the ground and a 2,600-gallon tank used to water the plants.

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The cultivation setup was hidden amid rolling hills on a 40-acre private property. Stuart would not identify the property’s owner because the investigation is ongoing.

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