Yellow blooms of black mustard weed covering hills in Southern California

The bright yellow blooms of the black mustard plant fill the hillsides of Calabasas along the 101 Freeway corridor.

The bright yellow blooms of the black mustard plant fill the hillsides of Calabasas along the 101 Freeway corridor.

People hiking along the trails in Fairview Park are dwarfed by the tall stands of black mustard in Costa Mesa.

Fields of black mustard, growing as high as 10 feet, are covering the fields and slopes of Fairview Park in Costa Mesa.

A pedestrian wearing a yellow shirt blends in with the mustrad growing along the trails at Fairview Park in Costa Mesa.

Black mustard grows along the hiking trails in Griffith Park.

Black mustard grows along the hiking trails in Griffith Park.