JEFFERSON COUNTY, Colo. -- Residents of a Jefferson County subdivision north of Golden were allowed to return home Wednesday evening after a wildfire threatened their homes.

Two grass fires joined a short time after they were first reported at about 5:30 a.m. They were believed to have been started by a passing train.

As of 8 .m., the fire was nearly 100 percent contained at less than 100 acres, officials said. The smoke cleared enough Monday afternoon to give firefighters a better idea of the size.

The fire burned just west of Highway 93 and off Highway 72, at the mouth of Coal Creek Canyon, officials said. It threatened homes in the Blue Mountain subdivision.

Small Spotter Plane Veers Off Runway

A single-engine spotter plane that was helping with the fire veered off the runway at Jefferson County Airport Wednesday morning as it was attempting a takeoff, but the pilot escaped unharmed.

Pictures from AirTracker7 showed the plane off to the side of the runway, with at least one wheel missing. The crash caused extensive damage to the wings and landing gear, but most of the plane was intact.

It was not immediately known what caused the plane to run off the left side of the runway, but Westra said the area was hit by the same gusty winds that fanned the fire.

The pilot was identified as identified as Steven Whary from San Angelo, Texas.

Whary had already made one slurry drop and had landed at the Jeffco Airport to refill his tanks. He was in the process of departing for a second trip, when about 1,000 feet down the runway, the plane went off the south edge of the strip, which bent the wings and landing gear.

The accident did not produce a fire.

Officials said the Air Tractor aircraft can hold 800 gallons of slurry, but the Whary was carrying only 600 gallons because of wind conditions.

A helicopter from Rocky Mountain Interagency Helitack, based at Boulder Municipal Airport, was also used to fight the fire.

Train Sparks Cause Fire?

The fires were apparently sparked by a passing train that runs parallel to Highway 72, Jefferson County Sheriff's Department spokeswoman Jacki Tallman said.

Union Pacific officials called 911 and were the first to notify authorities about the fire.

"Union Pacific really stepped up to the plate there and notified us right away as soon as they saw the sparks, and got their train stopped, and took responsibility for what was going on," said Jefferson County Sheriff's Department spokesman Jim Shires. "Without that taking place, we could not have gotten fire crews in there as soon as (we did), and notified people, because it was 5:30 in the morning. People were still asleep."

7NEWS reporter Sean McLaughlin said the probe was focusing on the train.

The 103-car train was coming from a western Colorado coal mine, heading to a power plant in Illinois when the blaze started, McLaughlin said.

"I just talked with a Union Pacific spokesman who told me they're looking at the possibility of a failed electric brake," said McLaughlin

Such a failure would send sparks flying from the locomotive's wheels. Those sparks could obviously start a fire, considering the very dry conditions.

As for any financial responsibility from Union Pacific, McLaughlin asked if Union Pacific would reimburse local firefighting companies who battled the blaze.

He was told, "That would be a case-by-case basis. We would have to look at that."

The investigation into how the fire started could take a matter or hours, or a matter of weeks, McLaughlin said.

Union Pacific has pulled the train in question from its route. It now sits at a Denver rail yard, where railroad officials will look into how it could have sparked the fires.

Homeowners Get Reverse 911 Call

Jefferson County implemented its reverse-911 system early Thursday morning, calling 111 homeowners in Blue Mountain Estates and telling them to evacuate.

A half-awake Cristina Bishop thought she was seeing a beautiful sunrise when she caught a glimpse of bright orange outside her bedroom window when she first woke up. But within a few minutes, she realized she was seeing flames and then there was a police officer knocking on the door telling her to evacuate.

Her two children, ages 2 and 5, were roused from their beds by her yelling.

It was supposed to be her son's first day of kindergarten but instead he and her daughter were standing in their pajamas along a road north of the fire watching a helicopter drop water on the blazes.

"I don't think he's going to make it," said Bishop, who said her neighbor's house was on fire by the time she left.

Earlier in the day, the fire had climbed up the ridge where roughly 12 to 15 very large and very expensive homes sit. Some homeowners were seen hosing off their lawns and decks as flames licked at the trees that border their property.

"It was extremely close to the homes. My understanding is that one of the hot tubs covers actually caught fire, so it was very very close to the homes that are up there. Some of them, it was at their doorstep," Shires said.

Highway 72 at Highway 93 was closed briefly to allow emergency vehicles access to the area.

The fire burned along Highway 72 at Plainview and Blue Mountain.

There were four separate fire departments at the scene, working the blaze, including Arvada, Rocky Flats, Coal Creek and Golden Gate.

The land is steep and rugged, making it tough for firefighters to get around it and build containment lines, 7NEWS reported.

No injuries were reported as a result of the fire.

The fire created a lot of smoke, which drifted into the metro area.