In January 2025, the Los Angeles area experienced devastating wildfires, notably the Palisades and Eaton fires, which collectively burned over 50,000 acres.

These fires resulted in at least 29 fatalities, forced more than 200,000 residents to evacuate, and destroyed or damaged over 12,000 structures.

Exacerbated by prolonged drought, low humidity, and powerful Santa Ana winds, the fires spread rapidly. 

After weeks of weathering dangerous fire and evacuation orders, residents then faced the threat of incoming heavy rains.

While the rains were welcomed in hopes they would sequester the flames, they also created a new risk of post-fire debris flows. 

What is a debris flow? 

Debris flows, often termed “mudslides” by the media, are a form of rapid mass movement in which loose soil, rock and sometimes organic matter combine with water to form a slurry that flows downslope.  

These fast-moving landslides  can occur during short duration, high intensity rainstorms when rain falls on burned hillsides.

The absence of vegetation and the presence of water-repellent soils formed during severe fires increase the likelihood of these dangerous flows, which can pose significant threat to public safety, infrastructure, and natural resources.

To mitigate these risks, the California Geological Survey (CGS), a division of the Department of Conservation (DOC), plays a vital role in assessing and mapping post-fire hazards. 

How the California Geological Survey Helps Keep California Safe After Wildfires 

Following major wildfires, CGS collaborates with CAL FIRE to form Watershed Emergency Response Teams (WERTs). The California Governor’s Office of Emergency Services (Cal OES) supports implementation of WERT hazard mitigation recommendations via the Watershed/Debris Flow Task Force. 

These teams conduct rapid assessments of burned areas to evaluate potential geologic hazards, including debris flows, rockfalls, and flooding.

The findings are then shared with local emergency managers, policymakers, and the public to inform response and mitigation efforts.

CGS’s post-fire debris flow susceptibility mapping provides emergency responders and communities with critical information about areas most at risk. These maps help guide evacuations, road closures, and life-safety and property protection efforts, supporting both immediate response and long-term resilience planning. 

Interagency Collaboration to Safeguard Communities 

By partnering with CAL FIRE, Cal OES, local governments, and other state and federal agencies, DOC enhances California’s ability to anticipate and mitigate post-fire hazards. This collaboration ensures that communities receive timely, science-based guidance to reduce risks and protect lives and property. 

In the aftermath of the fires, WERT teams were deployed to assess damage and identify potential hazards. Their findings have been instrumental in guiding local response efforts and helping communities prepare for the upcoming rainy season. These assessments also provide valuable data for legislators and agency partners involved in wildfire recovery and risk reduction efforts. 

Leadership in Action: A Firsthand Look at the Damage 

Before even settling into her new office, newly appointed DOC Director Jennifer Lucchesi visited the burn sites alongside California Natural Resources Agency (CNRA) Secretary Wade Crowfoot, and State Geologist Jeremy Lancaster. Their visit highlighted the state’s commitment to rapid response and recovery efforts. 

Resources 

CGS offers several resources to assist decision-makers, emergency managers, and the public in understanding and preparing for debris flow hazards: 

• Watershed Emergency Response Team (WERT) Reports – Detailed assessments of fire-impacted areas to evaluate post-fire hazards and inform response strategies. 

• Recent Burned Watershed Hazard Assessments – Reports on the latest fires and their associated risks to support data-driven decision-making. 

• Landslide Maps and Data – Interactive maps displaying landslide-prone areas across California to aid in mitigation planning. 

Stay Informed and Prepared 

Residents within and downstream of areas recently burned by wildfire  are encouraged to stay informed about potential debris flow hazards, especially during the rainy season following wildfires. Monitoring local weather forecasts, heeding evacuation orders, and utilizing available resources can significantly improve safety and preparedness efforts. 

For more information on CGS’s programs and resources, visit: http://www.conservation.ca.gov/cgs

Read about previous years’ post-fire debris flow work here.

By leveraging scientific expertise and fostering interagency collaboration, the Department of Conservation remains committed to protecting Californians from the threats posed by post-fire debris flows and ensuring that decision-makers have the tools they need to make informed decisions.