Cal Fire issued a statement on the fatality, saying: “The Mendocino Complex Unified Incident Commanders for Cal Fire, and the United States Forest Service are deeply saddened to report the death of a firefighter on the Mendocino Complex.”
They noted that a fact finding investigation is currently underway to determine the exact circumstances of the fatality.
Notification of the next of kin is currently in progress.
The Mendocino Complex Fire, which includes the River Fire and the Ranch Fire, has scorched a total area of more than 344,890 acres.
The Ranch Fire was 59 percent contained at 8am local time (4pm BST) on Monday morning, at a size of 295,970 acres.
The River Fire is now reported to be 100 percent contained, and has brunt an area of 48,920 acres.
The fire has nevertheless destroyed 146 homes thus far, and is not expected to be fully contained until September.
The Ranch Fire is expected to become California’s first, single fire to burn over 300,000 acres.
The fatality marks the sixth firefighter to be killed in California’s wildfires this year alone.
Eight civilians have also been killed in the blazes across the state.
This is the first fatality caused by the Mendocino Complex Fire, which is located north of Clear Lake.
A total of eight people have been killed in connection with the Carr Fire, including two firefighters and four civilians.
A PG&E employee was killed in a vehicle incident while working to restore services to areas affected by the Carr Fire on August 4.
A Cal Fire heavy equipment mechanic was also killed in a traffic accident while working on the Carr Fire.
Mandatory evacuations remain in place across the state for around 11,120 individuals.