A cluster of small roadside blazes Tuesday combined to form a roughly 25-acre brush fire that scorched a rocky hillside in Nuevo.
The non-injury spot fires were reported at 11:55 a.m. Tuesday in the area of Ramona Expressway and Rider Street, according to the Riverside County Fire Department.
The agency said multiple engine and hand crews were sent to the area and encountered three separate fires, initially amounting to less than two acres.
The spot fires, however, merged within minutes and raced up a hill, east of the expressway.
One fire captain first estimated the brush fire at nearly 100 acres, but after two Cal Fire air tankers and a water-dropping helicopter arrived and got an overhead look, the brusher was determined to be 20-25 acres in size, according to reports from the scene.
No homes or others structures were immediately threatened.
The California Highway Patrol said motorists called just after the fires erupted, saying a heavy-loaded truck was throwing sparks along the expressway, igniting the extremely dry roadside vegetation amid 100-degree heat.
Officers shut down the expressway, between Rider to the west and Lakeview Avenue to the east, as a public safety precaution.
Detours were in place.