The Delta Fire ignited on September 5, 2018, at approximately 12:51 PM PDT, 2 miles north of Lakehead, California. The fire rapidly grew in size, crossing over Interstate 5 between Lakehead, California, and Castella, California, which forced the interstate to be shut down from September 5 to September 10. On September 10, the fire merged with the nearby Hirz Fire to the east, and by September 11, the fire was only a few miles away from burning into the already-contained Carr Fire to the southwest.^[2]

On September 12, the Delta Fire reached 57,253 acres (232 km²) and was only 17% contained. On September 13, the northern flank of the fire flared up again and shut down Interstate 5 again for six hours during the afternoon. During the next few days, the Delta Fire continued to grow in size, albeit at a slow rate, while firefighters continued making progress on containing the wildfire, with the fire reaching 60,277 acres (243.93 km²) and 76% containment by September 17.^[3] On September 18, firefighters had contained most of the Delta Fire's northern flank, while flames on the fire's southwestern flank continued to spread, nearly reaching the Carr Fire's burn area.^[4] Late on September 19, the Delta Fire had grown to 60,592 acres (245.21 km²), while containment increased to 88%, with the southwestern flank of the wildfire being the only active portion of the fire.^[1] On September 24, the Delta Fire had grown to 60,751 acres (245.85 km²), while containment increased to 98%.^[1]

On September 25, a spot fire broke out in Bear Gulch, outside of the southwestern perimeter of the Delta Fire, which quickly reached 1,000 acres (4.0 km²) by the next morning.^[5] On September 27, a second, smaller spot fire had broken out to the south of the larger spot fire, situated south of Damnation Creek, which was estimated at 14 acres (0.057 km²).^[6] The first spot fire continued to spread uncontained, while the main body of the Delta Fire was contained; by September 29, the first spot fire had exceeded 2,376 acres (9.62 km²) in size, increasing the total burn area of the Delta Fire to 63,093 acres (255.33 km²), and dropping the overall containment of the Delta Fire to 97%. The spot fires were at 0% containment.^[7][1] On September 30, the Delta Fire expanded to 63,293 acres (256.14 km²), with containment remaining at 97%.^[8] The fire did not experience any further growths for the next several days, while containment generally remained at 97% up until October 5.^[9] Afterward, the Delta Fire experienced another small growth, increasing to 63,311 acres (256.21 km²). On October 7, the Delta Fire was fully contained, without any further increases in size.^[10]

The fire was determined to be man-made, although the exact cause remains unclear.^[11] On May 5, 2021, Shasta County District Attorney, Stephanie A. Bridgett announced that a Cynthia Ann LeRoux had been arrested and faces charges for starting the Delta Fire.^{[citation needed]}

• 2018 California wildfires
  • Carr Fire
  • Hirz Fire

• Record Searchlight Delta Fire Updates
• ArcGIS Delta Fire Activity Map
• InciWeb Delta Fire Map Archived 2018-09-19 at the Wayback Machine
• Cal OES Delta Fire Live Map