When the fire began, hot and dry conditions prevailed over the region: according to the National Weather Service temperatures were in the low or mid-90s °F and relative humidity levels hovered around eight or nine percent.

[17][18] Following an 11-month investigation, on Friday, June 16, 2023, 71-year-old resident of Mariposa County Edward Frederick Wackerman was arrested on suspicion of starting the Oak Fire.

The investigation that resulted in Wackerman's arrest involved the FBI, the National Park Service's law enforcement division, and Cal Fire.

Authorities did not describe a method or motive for the arson, though Mariposa County sheriff Jeremy Briese did disclose that he believed Wackerman had previously been employed as a firefighter.

[17] The fire affected the Southern Sierra Miwuk Nation, a federally unrecognized Native American tribe indigenous to the region.

The Oak Fire threatened multiple communities in rural Mariposa County, including Lushmeadows, Midpines, Jerseydale, and Bootjack.

[5] An evacuation center was established at New Life Christian Fellowship church, but continued rapid fire spread forced officials to move it to Mariposa Elementary School,[5] where more than 100 people checked in and almost half of that group chose to spend the night on July 24.

[29][30] Smoke from the Oak Fire spread widely, causing authorities to issue air quality advisories even in distant areas, such as Barstow and the Victor Valley.

[5] Prevailing winds pushed smoke northeast, prompting air quality warnings for multiple days in a row for western Nevada.

[6] In parts of the Sierra Nevada such as the Lake Tahoe Basin, where the smoke was particularly thick, it caused poor visibility and the air quality indices reached unhealthy to hazardous levels.