The fire started around 2:30 pm on Thursday off Live Oak Road in the Yaqui Gulch area, a few miles west of downtown Mariposa.
Video from the county's sheriff office shows the blaze burning through the trees and sending that thick smoke billowing into the sky.
Firefighters and sheriff's deputies responded to the fire that has closed Yaqui Gulch Road from Hwy 140 to Old Highway Road.
As of Friday morning, the fire has charred 250 acres and is 25% contained.
No structures are under threat at this point, and no one has been injured.