Update: Norton Fire spreads to 55.2 acres in Contra Costa County, remains 40% contained
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Updated: 10:32 p.m. May 21
First discovered: 5 hours ago, 5:26 p.m. May 21
Initial location: Nortonville Road and Black Diamond Road, Clayton, Contra Costa County, Calif.
Fire unit: Cal Fire Santa Clara Unit
Fire type: Wildfire
Fire name: Norton Fire
Norton Fire initially started today at 5:26 p.m. at Nortonville Road and Black Diamond Road, Clayton in Contra Costa County, California.
Since its discovery five hours ago, it has burned 55.2 acres, an increase of 15 acres since the last update. As of Thursday evening, a crew of 74 firefighters effectively contained 40% of the fire. The cause of it remains under investigation.
Nine engines, two helicopters, two dozers and two hand crews will continue to combat the blaze. According to Cal Fire, "Numerous firefighting air tankers from throughout the State are flying fire suppression missions as conditions allow."
See live video from the area:
Https://cameras.alertcalifornia.org/?id=Axis-Kregor
Fire containment
What does it mean for a fire to be 40% contained?
The percentage indicates how much of the fire perimeter has been surrounded by a control line. In this case, it means that 40% of the wildfire is halted from spreading, while 60% is still uncontrolled.
Containment is part of a larger plan for managing a wildfire. It is normally expressed as a percentage and it refers to how much of the fire perimeter has been surrounded/enclosed by a control line that firefighters create. The containment percentage indicates a certain level of control, but it doesn't always correlate to safety level. Also, it's important to note that containment doesn't mean a fire is out.
How is containment measured?
The incident's central command constantly receives progress reports from firefighters on the ground. As the fireline is constructed, inspected or reinforced, mappers record those details to adjust the containment percentage. The percentage tells the public how much of the fire perimeter is believed to not go beyond the control lines.
Source: Cal Fire
United Robots Sacramento
This story was originally published May 21, 2026 at 5:44 PM.