LAKE ARROWHEAD – A crowded neighborhood in the San Bernardino Mountains went up in flames during a wildfire last fall because the homes were close together, had wooden roofs or had other vulnerabilities, new reports concluded.

A shower of embers rather than a wall of flame was responsible for igniting most of the 199 homes that were damaged or destroyed in the Grass Valley fire near Lake Arrowhead, a U.S. Forest Service report concluded.

The fire began on Oct. 22 and was contained on Oct. 26. Twin reports released Tuesday examined the fire's behavior and damage.

The blaze, roaring through drought-stricken brush and fanned by Santa Ana winds, hit a dense residential development 60 miles east of Los Angeles. But only six homes actually were engulfed by the fire, a report executive summary said.

The rest were caught in a “domino effect” as firebrands from burning brush or homes hit other residences, the report said.

Firefighters were “overwhelmed” in trying to stop the fire's spread through the subdivision because several homes were burning at the same time, the executive summary said.

“However, more homes would have burned without their intervention,” the summary said.

A sister report concluded that firefighters were better able to protect homes and made more progress against the fire in areas where dead trees had been removed.

Years of drought weakened trees in the area and left them vulnerable to bark beetles. More than 186,000 dead trees were removed from 2003 to October 2007, the report said.

In areas where that forest thinning had taken place, the fire burned more slowly and with less intensity, the report concluded.

---