A quarter-acre field fire off of Stringtown Road near Carpenter Creek Road was extinguished Wednesday morning, Forest Grove Fire & Rescue said.
As of about 9:30 a.m., firefighters were still on scene extinguishing hotspots.
The fire was located between the communities of Watts and Dilley.
"The cause of this mornings fire was from farming equipment hitting a rock while processing the hairy vetch crop field," FGF&R later said.
The agency added their thanks to a local farmer who was passing by with a fire trailer who stopped and kept the fire in check until firefighters arrived.
A Red Flag Warning ended at 8 a.m. Wednesday.
"No lightning across the Northwest Oregon Forest Protective Association last night," Oregon Department of Forestry Forest Grove District Forester Mike Cafferata said in an email Wednesday morning.
This story has been updated with a photograph and additional information from FGF&R
