The raid of several connected marijuana gardens this week revealed the continued presence of what appear to be Mexican growing operations in Nevada County, sheriff's officials said.In the biggest pot raid of the year, Nevada County sheriff's deputies seized more than 1,600 marijuana plants in the South Fork Yuba River canyon Wednesday, near the Highway 49 bridge.No one was arrested in the raid, Capt. Ron Smith of the Nevada County Sheriff's Office said."We believe it was a commercial drug trafficking operation, but it appeared to be abandoned," Smith said. "There was chicken wire, trash and garbage, showing people had been …