The current fires have forced the state to use every resource available. There are roughly 5,300 full-time firefighters with Cal Fire, who, along with 1,700 seasonal firefighters throughout the state, are often the first to the front lines of the state’s wildfires. The state also relies on thousands of federal firefighters based in California who respond to fires in national parks and forests. And there are 3,500 inmate firefighters who live in camps throughout the state and are routinely called up — nearly 2,000 were deployed on Tuesday.

This summer, firefighters from more than a dozen other states, including Maine, New Jersey, Michigan and South Dakota, have all come to assist.

“There are more fires that are burning more expansively over longer periods of time, and there are fewer resources available to respond, especially to respond quickly,” said Carroll Wills, a spokesman for the California Professional Firefighters, a statewide union. “And local agencies often feel like they can’t send crews to help, because their resources are scarce and they feel like they have to be able to protect their home front.”

Federal and state fire officials prioritize which fires need the most resources largely based on how many homes are threatened, but that can change in mere hours. This means officials are constantly reassessing the demands for crews and equipment. Fire officials regularly ask for “mutual aid” from other departments, who also must anticipate the possibility of new fires.

“As large as our firefighting resources are, they’re limited, and we’re rapidly approaching the limits of what our personnel can handle,” said Marti Witter, a fire ecologist with the National Park Service. “Everyone’s in the air, everyone’s on the ground, and the fire’s just getting bigger. So it’s pretty extreme.”

Just in the last two weeks, several crews have responded to the Cranston Fire in Southern California, driving for 10 hours to the Carr Fire in Redding and then heading to the Mendocino Complex Fire about 200 miles south, Mr. Cox said. The firefighters are supposed to get a day off every 14 days and another two after three weeks. That does not always happen, Mr. Cox said.

Even as firefighters travel from one end of the state to another, they move quickly: Cal Fire says there is a maximum of 18 hours in “reflex time,” from the moment a crew is ordered somewhere until the time they arrive. Crews routinely drive all night only to start battling flames in a new location shortly after dawn.