A 6 a.m. grass fire broke out on a steep hillside along Vichy Hills Road south of Ukiah Monday.

Flames burned about one acre before firefighters from three agencies put it out, said Ukiah Valley Fire Capt. Pete Bushby.

The cause was under investigation Monday, including whether it could have been sparked by an SUV parked precariously on the steep side of the hill where the fire burned, Bushby said.

The SUV was parked on an area of the hillside that was so steep it appeared it might roll, Bushby said.

Cal Fire and Ukiah firefighters also responded.

Initial reports from the CHP indicated the vehicle also may have been involved in the fire.

Further information from the CHP wasn't available early Monday.