The Topanga Fire, Part I: Rain, Wind and Fire.
Wednesday, March 29, 2006
Updated May 5, 2011 (Before/After Photos)
Copyright © 2011 Gary Valle'. All Rights Reserved.

Note: The "T numbers" specified are relative to the start of the Topanga Fire on Wednesday, September 28, 2005 (T+0). The active spread of the fire ended the afternoon of Friday, September 30 (T+2).

Nearly two weeks after the Topanga wildfire burned 24,000 acres of ecologically diverse Mediterranean habitat northwest of Los Angeles, the charred remains of thick chaparral continued to smolder. Around me black fingers of Yerba Santa, Ceonothus and Chokecherry projected from the barren earth, their skeletal remains reflecting the fury of the fire. Running through the stark landscape, it was hard to accept that fire is a much a part of the environment as the wind and the rain.

Southern California's annual cycle of rain, drought and wind promotes periodic fire. Winter rainfall is extremely variable, and Summers are hot and dry. The average annual rainfall in downtown Los Angeles is about 15 inches, but it is an average of extremes. Year to year rain totals can differ by more than 10 inches, and it is common for the area to have less than an inch of rain from May to October. In the Fall, our low elevation basin geography combines with post-frontal high pressure in the Great Basin to produce multi-day periods of strong, compressionally heated "Santa Ana" winds.

The rain season of 2004-2005 was the second wettest on record for Los Angeles. From July 1 to June 30, a total of 37.25 inches of rain was recorded — more than twice the normal amount. Spring growth was phenomenal. Large areas of Ahmanson Ranch were blanketed with black mustard several feet tall. In some areas of Las Virgenes Canyon milk thistle (Silybum marianum) towered above the heads of hikers and runners like Klingon corn. Desiccated by months of heat and drought, these, and other rain enhanced understory materials, would burn with frightening ease.

The Topanga Fire was reported to Los Angeles County Fire at 1:50 P.M. on September 28, 2005, near the 118 Freeway and Topanga Canyon Rd. Wind driven, the fire spread rapidly to the southwest, running seven miles in seven hours. Erratic and extreme fire behavior was reported on the 29th (T+1), as the fire expanded from approximately 4300 acres to 20,650 acres. Unstable fire behavior continued on the 30th, as the fire transitioned to a topography driven fire. Spread of the fire essentially ended October 1 (T+3) at 24,175 acres, and full containment was reported at 6:00 P.M. on October 4 (T+6).

Three homes, three commercial buildings, various outbuildings, and other improvements were reported lost. Through the efforts of firefighters, the value of property saved through fire suppression was estimated at $804,250,000. Property saved due to vegetation modification, defensible space clearance, and fire resistant construction was estimated at several billion dollars.

CDF-FRAP fire perimeter data lists 23 fires over 300 acres that have burned portions of the Topanga Fire area since 1927. This sequence of slides shows these fires. (Requires Flash Player 8.)

The northern one-third of the fire area, in the area of Santa Susana Pass, and to the southwest, was burned by the Oat Fire (1981), and then some sections were burned again in the Box Canyon Pioneer (1985), Hummingbird (1985), Keuhner (1988), Chatsworth (1993), and Simi (2003) fires.

The southern half of the fire area, including Bell Canyon, Ahmanson Ranch, Las Virgenes, Cheeseboro and Palo Comado Canyons, and Simi Peak, were burned in the Dayton Canyon Fire (1982).

According to CDF-FRAP fire perimeter data, a large area extending along the Simi Hills from northeast of upper Las Virgenes Canyon through Rocketdyne to Black Canyon, had not burned since the Clampitt Fire (1970). In addition, a discontinuous area extending from the head of Las Virgenes Canyon west to the northern flanks of Simi Peak had not burned since the Devonshire-Parker Fire (1967).

These 35+ year-old stands generally correspond to areas of very high hazard (red) mapped in this graphic of CDF Fuel Rankings. My own "on the ground" impressions of burn severity roughly paralleled these fuel rankings as well.

In an area north of Simi Peak, the fire intensity was such that nearly all plant materials were consumed down to the mineral earth. This was also the case on slopes of similar aspect northeast of Sage Ranch.

These before and after views of several locations within the fire area characterize the severity of the fire. The "after" views were taken shortly after the fire area was reopened to the public, and 5+ years after the fire.

The capriciousness of fire was well illustrated in upper Palo Comado Canyon, southeast of China Flat. Here, an island of brush remained in an area that had been severely burned.

Ahmanson Ranch's Oak and Riparian Woodlands and Grassland habitats distinguish it from the various chaparral and sage scrub habitats that make up the majority of the fire area.

In contrast to the rapid replacement strategy adopted by chaparral shrubs, Valley and Coast Live Oaks deal with fire in a simple, stoic fashion — they survive it. This is due in part to their thick, convoluted bark and ability to quickly regenerate foliage.

However, not all oaks survive. Oaks weakened by disease or otherwise compromised may fall victim, sometimes painting a ghostly image of the tree in ash. (Upper Cheeseboro and Las Virgenes Canyons, respectively.)

What about the animals? Less mobile, ground dwelling animals probably had the highest mortality. On October 1 (T+3), a friend reported "dozens of dead animals, mostly rabbits" in an area on the eastern margin of Ahmanson Ranch. Several days later (T+15) few carcasses remained, and I saw only isolated instances of dead animals on or near trails. With the exception of the carcass of a deer, most of these were rabbits or small rodents. The quail population may have also been significantly impacted.

In the weeks following the fire, I have seen several coyotes and the tracks of a few deer, but very few ground squirrels, rabbits, or quail.

Remarkably, within days of the start of the Topanga Fire, and while the fire still smoldered in some areas, this Yerba Santa along the Hummingbird Trail was already replacing its scorched leaves.

Less than a month after the fire (T+27), following a drenching October rain, the muted browns and blacks of the burned grasslands of Ahmanson Ranch erupted in a lime-green blanket of new growth. Shortly thereafter (T+36), several day-old growth was observed on both Coast Live Oaks and Valley Oaks. Less than two months (T+48) following the fire, crown sprouting of Yerba Santa and Laurel Sumac had begun at Sage Ranch.

Notes:

Since its acquisition by the Santa Monica Mountains Conservancy in late 2003, Ahmanson Ranch is referred to as the Upper Las Virgenes Canyon Open Space Preserve.

The GIS products Global Mapper, TatukGIS. and Xport Pro were used to create fire area graphics.

References for Part I:

After Action Report Topanga Fire CA-LAC208724 28, Sept 2005 – 6, Oct 2005 (PDF)

Fire History Perimeter data is from the Fire and Resource Assessment Program, California Department of Forestry and Fire Protection, Information and Data Center, Data : Fire Perimeters.

Topanga Incident Perimeter data is from the Geospatial Multi-Agency Coordination Group (GeoMAC). Perimeters are collected in the field by a variety of means, including infrared flights, and by using a GPS unit to map the perimeter. Please NOTE: GeoMAC only displays perimeter data as they are submitted by field offices.