The "Farm Fire" was reported just after 1 p.m. in the area of Caliente and Ranchero roads, near the 15 Freeway.
It was initially estimated at 20-30 acres, but was spreading rapidly and some structures were threatened.
Multiple departments, including San Bernardino County Fire and state and federal agencies, were sending air and ground resources to fight the flames.
By around 3 p.m. it appeared firefighters had a good handle on the blaze, which continued to smolder with only a few hotspots of active flames.