The first blaze sparked just after 2:30 a.m. at Avenue 388 and Highway 201 near the town of Yettem.
Firefighters say a few old greenhouse structures caught fire.
Tulare area California Highway Patrol officers and Tulare County sheriff's deputies joined the investigation after a second pallet fire was found burning nearby.
The greenhouses were not currently being used for growing plants, officials said.
One of the fires caused a power line to fall, and crews were working to douse the flames. There was no immediate threat of spread, firefighters say.
The cause of both fires is under investigation.