RIVERSIDE (CBSLA.com) — Fire crews in Riverside on Saturday evening were fighting a brush fire that broke out near the Santa Ana River bottom.

The fire was first reported at about 2:30 p.m. near Beacon Way and Ladera Lane, just outside Fairmount Park.

By 6:30 p.m., the fire had grown to 35-40 acres, authorities said.

The fire was 50 percent contained and was threatening some structures, firefighters said.

Units from Cal Fire and Corona Fire Department were on the scene, providing protection to nearby houses.

No evacuations had been ordered initiated, and no injuries were reported, fire crews said.

The cause of the fire was under investigation.

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