The fire erupted in dry, windy conditions along Interstate 15 in the Cajon Pass and quickly spread to more than 350 acres.
The California Highway Patrol ordered I-15 and part of Highway 215 shut down indefinitely.
"There is no way around it. I am just going to have to wait it out" Scott McKelvery of San Diego, who was on his way to Las Vegas, told The (San Bernardino County, Calif.) Sun after he pulled over in San Bernardino.
The San Bernardino County Sheriff's Office ordered homes in Mathews Ranch evacuated.
KCBS-TV in Los Angeles said five air tankers had been dispatched to the fire.
Parts if inland Southern California were under a red-flag warning Monday as high pressure heated the region up well into the upper 80s.