Both fires began on August 19, 2020, and burned a combined total of 175,019 acres (70,828 hectares) before the complex as a whole was declared 100 percent contained on January 6, 2021.

The Castle and Shotgun fires were both begun by lightning, part of a 'siege' of hundreds of wildfires caused by dry thunderstorms across California in mid-August 2020.

The Castle Fire is notable for its devastating effects on native sequoia (Sequoiadendron giganteum) groves in the southern Sierra Nevada.

[3]: 80  The 60-mile-per-hour (97 km/h) winds pushed the fire through the 530-acre (210 ha) privately-owned Alder Creek Grove of giant sequoias, killing an estimated 80 or more trees.

[12] The area remains at risk for mud flows and flash floods due to the charred soil being unable to absorb water.

A 2021 report led by National Park Service scientists concluded that over 7,500–10,600 mature trees, 10–14 percent of the species' population, had likely been lost in the fire.

[2] In virtually every grove affected, extensive Giant Sequoia regeneration thrived especially in places where the fire was severely hot and had killed the most trees.