A Labor Day to Remember

On Labor Day, September 6, 2010 at 10:00 am, 10 miles west of Boulder, an errant spark from a fire pit ignited what would become the most destructive and expensive fire in Colorado’s history. A record 169 homes were lost, totaling an estimated $217 million. Fortunately, no human lives were lost. Within hours of ignition, the blaze rapidly encompassed thousands of acres, burning grasses, trees, homes, and wildlife. One hundred percent containment was achieved after 11 days, burning 6181 total acres.

Over 3,500 residents were forced to evacuate their homes, and by the 5th day of the fire 1,100 firefighters were working to contain the blaze. After 11 days, firefighters achieved complete containment of the flames.


Photo above: Smoke from the Fourmile Fire to the north of the Flatirons rock formations. Photo credit: Joe Gardner


Firefighter near burning tree

"It went from literally just a small spiral of smoke that I wasn’t slightly concerned with to a full blown federal incident… all within about 18 hours."

"Everything was so dry, no moisture, whatsoever. So as soon as anything hit...boom, it just went up completely in flames because the needles were so dry and they were so close together."

-Kitty Stevenson, Sugarloaf resident, Firefighter 2 , Emergency Technician B, Chief Medical Officer

Photo (right): Firefighter near a burning ponderosa pine. Photo credit: Kitty Stevenson


landscape view of fourmile fire

Photo above: View of the Fourmile Fire from Sunshine Canyon Drive. Photo credit: Meredith Gartner


Why was this fire so destructive?

The extremely hot and dry weather preceding the Fourmile Canyon Fire created the perfect conditions for a catastrophic wildfire.  Strong winds over 40 mph pushed the fire in new directions and prevented air tankers from being able to fly over the blaze.  The dense forests in the area helped fuel the blaze and create a more intense fire.


Sunshine Canyon developed dense forests of ponderosa pine during the 1900s. This shift from relatively open woodlands to dense forests provided abundant fule for the Fourmile Canyon, making it more severe. The house in the bottom right of the 1985 photo (below right) burned in the fire and its remains are visble in the 2011 photo.


Photo left: Sunshine Canyon in 1905. Photo credit:J.P Sturtevant 1905 Photo right: Sunshine Canyon in 1985. Photo Credit: TT Veblen & DC Lorenz 1985

Sunshine Canyon in 1905Sunshine Canyon in 1985


Sunshine Canyon in 2011

While this fire wreaked havoc on homes and property, its intensity and behaviors were consistent with the natural fire history of the area.  It exhibited a mosaic of effects where some areas were mildly burned and others burned severely.  Severely burned areas occurred mostly at mid and high elevations, steepe slopes, and north-facing slopes. 


Very severe parts of the fire blackened forests and destroyed and damaged homes, while areas that burned at low-severity mostly killed understory plants and seedling and sampling.


Photo above: Sunshine Canyon in 2011. Photo credit:TT Veblen 2011


Map of Fourmile Canyon Fire severity and burned/damaged structures. Destroyed and damaged homes were mostly in areas of the forest that burned at high severity.

"The Fourmile Canyon Fire destroyed so many homes primarily because it occurred in the Wildland Urban interface where there has been a great deal of residential development." - Dr. Thomas Veblen, Professor of Geography, University of Colorado

Map of Boulder Fourmile Fire

Map credit: Meredith Gartner and Teresa Chapman. Data source: www.bouldercounty.org


Very severe parts of the fire blackened forests and destroyed and damaged homes, while areas that burned at low-severity mostly killed understory plants and seedling and sampling.

Severly burned forestpatchy burn

Photo left: Area of high severity fire and high tree mortality in Fourmile fire. Photo credit: Meredith Gartner

Photo right: Area of moderate (or mixed) severity fire and patchy tree mortality in the Fourmile fire. Photo credit: Meredith Gartner


Post-Fire Hazards and Hope

Fires like the Fourmile Canyon Fire can play a beneficial role as part of the natural cycle of forests.  The loss of structures, livestock and human life can be devastating. 


Erosion and Flooding

When a high-severity fire burns vegetation risks of erosion and flooding dramatically increase.  The area of Fourmile Canyon that burned in September 2010 was ravaged by floods in July 2011. 


flood sign in boulder burned area


Environmental Concerns

Despite fires’ abilities to restore biodiversity, they also have negative environmental impacts.

The smoke produced by large fires is a disturbance to human and animal health. There is some debate as to the environmental and health impacts of chemical flame retardant dropped by planes to contain the fire.


Photo right:Caution sign after the FOurmile Fire. Photo credit: Meredith Gartner.


Planning Ahead

Many homeowners in the Fourmile Canyon area made regular efforts to thin and clear vegetation around their homes to reduce fire risks.  These “mitigation” efforts can increase the chances of a structure not burning but does not guarantee it.


Limiting risk through mitigation can be compared to wearing a seat belt. In a moderate collision, a seat belt will make a big difference but in a severe collision a seatbelt may not save a life.  Mitigation has saved homes in less severe fires during moderate weather but the Fourmile Canyon Fire occurred during extreme weather and became very severe.  Under these conditions, clearing vegetation may have a limited impact on home survival. 


Community Conversations

Ongoing conversations between scientists, architects, developers, and homeowners encourage the development of more fire-resistant homes located in lower fire risk areas. Building at lower elevations, on less steep south-facing slopes with non-combustible materials like cement and stucco help lower the risk of loss.


Buildings made mostly of concrete and metal, have a better chance of surviving fire. Organizations like Firewise Communities (www.firewise.org) offer advice on how to build more fire-safe structures.

home showing fire safe building materials

Photo above: Home that survived the Fourmile fire demostrates fire wise building materials. Photo credit: Merdith Gartner

Visit the University of Colorado Natural History Museum exhibit featuring the Fourmile Fire.


Acknowledgements: This website was funded with a University of Colorado Outreach Grant. We thank The University of Colorado Natural History Museum staff for their input and refinement of the presented material: Rebecca Wahlberg (interpretive Writer), Charles Counter (content and exhibit Coordinator), and Williams Moats (exhibit design and layout Technician). Researchers contributing to the material on this site include: Dr. Thomas Veblen (CU), Dr. Rosemary Sherriff (Humboldt State), Dr. Tania Schoennagel (CU, INSTARR), and Merdith Gartner (CU PhD Candidate).

Useful Links for more Fire Information

Teresa Chapman. Last updated 06.07.2012. Contact teresa.chapman@colorado.edu with questions about this site.