MARTINEZ -- Firefighters in Contra Costa County have controlled a two-alarm wildland fire outside Martinez that burned more than 30 acres early Thursday, a battalion chief said.

A fire was first reported by a citizen who saw flames from state Highway 4 near Franklin Canyon Road and McHarry Ranch Road at around 12:10 a.m., Battalion Chief Dave George said.

The fire burned for another two hours and took 18 units and 51 firefighters to knock it down, George said

"The fire was located in dense, thick, difficult to get to areas, and we were very thankful for the cell phone caller who noticed the fire and alerted us," George said.

Crews from Contra Costa County Fire Protection District, Cal Fire and East Bay Regional Parks assisted in the response.

There were no injuries and no damage caused to any structures, George said.

Parts of Franklin Canyon Road were expected to remain closed well into the morning, George said, and motorists on adjacent roadways should expect to see smoke and equipment after daybreak as firefighters continue mop up work in the area.

The cause of the fire was still under investigation.