SANTA ROSA, Calif. — Dr. Karen Relucio has heard reports of people digging into the ashes of their burned homes in recent days without gloves, wearing only shorts and T-shirts, looking for sentimental items that might have survived California’s horrific wildfires. And as the chief public health officer in Napa County, one of the hardest-hit places, she has used her office as a bully pulpit to urge them to stop, immediately.

“Just think of all the hazardous materials in your house,” she said in an interview. “Your chemicals, your pesticides, propane, gasoline, plastic and paint — it all burns down into the ash. It concentrates in the ash, and it’s toxic,” said Dr. Relucio, who declared a public emergency over the hazardous waste from the fires, as have at least two other counties.

California’s fires are far from out. They have killed at least 41 people and burned about 5,700 structures and over 213,000 acres since they exploded in force on Oct. 8 and 9 — record totals for a state that is used to wildfires. Thousands of firefighters are still at work fighting blazes and tens of thousands of people remain under mandatory evacuation from their homes, though fire officials have expressed cautious optimism about bringing the fires into containment.

But even as the smell of smoke still wafts through this area north of San Francisco, public health officials and environmental cleanup experts are starting to think about the next chapter of the disaster: the huge amount of debris and ash that will be left behind.