Search teams in Northern California after fire leveled entire towns have completed their work, having checked every burned building in the fire zone for human remains.

The search of nearly 18,000 fire-ravaged structures has not resolved the question of why nearly 200 people remain on the list of the missing. It is possible that the death toll will rise if some remains were overlooked or are found later in forests or other areas that were not searched.

Sheriff Kory L. Honea of Butte County, who led the search, said Thursday that he was “very optimistic” that people currently listed as unaccounted for would be found alive and that the death toll was close to final.