HOT STUFF: A Ripon firefighter prepares to tackle a grass fire along Austin Road near Highway 99 on Monday, May 12. The Ripon Fire Department was called in to help Manteca and Lathrop firefighters battle the blaze.

SPRAY IT: Manteca firefighters hose down a blaze on Highway 120 at the Union Road interchange Tuesday, May 13. The fire was one of two grass fires that halted highway traffic this week.

MANTECA — Several grass fires erupted along local highways this week, marking an uncommonly early start to the Valley’s fire season.

A windswept blaze burned more than 100 acres of grass along Highway 99 on Monday morning, May 12, billowing smoke and bringing traffic to a standstill for nearly an hour.

Fire erupted again around noon on Tuesday, this time along Highway 120, burning grass and trees on all four corners of the interchange with Union Road, which was temporarily closed down.

Though grass fires are a regular summer occurrence in San Joaquin County, firefighters say this week's blazes signal an especially early start to an annual problem.

“We’re experiencing an early fire season,” said Fred Manding, Interim Chief of the Lathrop-Manteca Fire District. “The grasses right now — I can’t believe how dry they are … these conditions are more common to July or August or September.”

Monday’s fire was first reported at 10:30 a.m. just north of the interchange between Highways 99 and 120, eventually spreading south past the Austin Road and the Highway 99 interchange.

Firefighters controlled the blaze within an hour, Manteca Interim Fire Chief Chris Haas said, while mop-up work continued well into the afternoon.

During the first half hour of the blaze, the smoke along the highway was so thick that fire officials shut down all southbound lanes of Highway 99 where it crossed 120 to prevent accidents and keep drivers from blindly passing into the flames.

Firefighters lined up to protect a row of business along Moffat Boulevard, including a propane company. Despite strong winds pushing the blaze south, firefighters were able to avoid any injuries or damage to buildings, Haas said.

Deputy Fire Marshal Marvin Mears said CalTrans workers mowing grass within 10 feet of the fire’s starting point are thought to have caused the blaze, but an investigation was still ongoing as of press time Thursday.

On Tuesday, the fire at Union Road and Highway 120 burned trees and grasses before it was fully extinguished five hours later.

Again, thick smoke forced firefighters and highway patrolmen to block the Union Road overpass for two hours while they brought the fire under control. The cause of that fire is also under investigation.

Mears said uncommonly low humidity this week made the grasses especially susceptible to fire, while high winds didn’t help firefighters control the blaze.

“I received information from one of the weather stations that (humidity) was at 9 percent (on May 12),” Mears said.

“At that level, it’s easy to light a fire with a cigarette or a spark from a lawnmower."