(CNN) -- Officials expect to contain a wildfire in San Bernadino County, California, by Tuesday night if conditions remain favorable.
The Ken fire -- named for a local freeway exit -- had scorched some 350 acres was 40% contained late Monday night, said Forest Service spokeswoman Angelica Mendoza.
The fire was first reported Monday afternoon in a mostly rural, sparsely populated area of the sprawling county in southeast California. Authorities do not know what started it.
More than 500 firefighters, 18 fire engines and 11 aircraft worked the blaze Monday, Mendoza said.
One firefighter suffered a knee injury. In addition, a ranch in the area was evacuated and at least one home was burned, Mendoza said.
A separate fire also in San Bernadino County consumed about three acres before it was contained, according to the county fire department.