The McCash Fire was one of multiple large wildfires, including the Monument and McFarland fires, ignited by thunderstorms in Northern California in late July. It was first detected on July 31 at about 7:00 p.m., burning in the McCash Fork drainage of Ukonom Creek (from which the incident got its name). The area was a rugged and inaccessible part of the Six Rivers National Forest.^[2]: 1 By the afternoon of August 2, the fire had burned 500 acres (200 ha) of primarily timber understory, brush, and grass near Bear Mountain. At this point, 172 personnel were engaged on the fire, including three hotshot crews, a group of smokejumpers, and two helicopters.^[3] The fire initially burned east, reaching the Marble Mountain Wilderness Area two miles (3.2 km) distant by August 5. At that point, mapping assessed the fire as having burned 1,161 acres (470 ha).^[2]: 1

A month after the fire's detection, it had burned 38,906 acres (15,745 ha). In the first nine days of September the fire's growth accelerated, reaching 69,725 acres (28,217 ha).^[4] At the height of the fire, firefighters employed nine aircraft: eight helicopters and a supervisory fixed-wing air attack plane.^[2]: 11

Between 1.2 and 1.4 inches (3.6 cm) of rain fell over the fire on September 18 and 19, temporarily miring firefighting operations with muddy roads and cloud cover. as the fire remained 22 percent contained.^[5][2]: 2 Though immediately followed by warm and dry conditions, the subdued fire activity following the wet weather meant that firefighters were able to engage the fire directly (see direct attack) on its northern, western, and southern flanks. The eastern side of the fire in the Marble Mountain Wilderness was held in check by old fire scars as officials opted for a confinement strategy instead of direct attack there.^[2]: 2

Containment of the fire reached 48% by September 27 as another weather system moved through the area and dropped 0.6–0.8 inches (1.5–2.0 cm) of rain. The incident management team characterized fire suppression operations as "largely complete" by September 29.^[2]: 2 All evacuation warnings and orders still in place were lifted on October 13, 2021, following minimal activity on the fire's part.^[6]

The McCash Fire was declared 100 percent contained by 6:00 p.m. on October 27, 2021.^[7] The cost of containing the fire was calculated at $53.3 million.^[8] The fire burned 94,962 acres (38,430 ha) in total; a post-fire environmental evaluation estimated that 53,636 acres (21,706 ha) had burned within the Klamath National Forest, 41,051 acres (16,613 ha) had burned within the Six Rivers National Forest, and the remaining ~200 acres (81 ha) had burned on private or other types of land.^[9]

The sole casualty of the McCash Fire was wildland firefighter and paramedic Marshall Grant Brookfield. Brookfield contracted COVID-19 and a fungal infection associated with wildfires and smoke inhalation while deployed to Orleans on the fire in September, passing at the age of 41 after several weeks in the ICU.^[10][11]

No structures were damaged or destroyed in the McCash Fire.^[12]: 11

The burned area emergency response (BAER) team assigned to the McCash Fire analyzed soil burn severity (SBS) across the fire footprint using remote sensing and soil data from the field. Separate from vegetation burn severity, soil burn severity is a qualitative metric based on the amount of remaining surface material, soil stability, and soil hydrophobicity. Soil burn severity influences post-fire runoff and debris flow issues. The McCash Fire's overall footprint was calculated to contain the following SBSs: 69 percent very low or low, 26 percent moderate, and five percent high severity.^[9]

• Monument Fire
• McFarland Fire