LOS ANGELES—A father and son have been sentenced to prison following convictions in a sweeping federal racketeering case in which prosecutors accused them as racist gang members who conspired to attack black people to force them out of a Southern California bedroom community.

Dozens of suspects were convicted in the case that marked the Justice Department's first time combining civil rights statutes with racketeering and drug laws to take on racially motivated gang activity, federal prosecutors said.

Santiago Rios, 48, who authorities said was the leader of an Azusa gang that took orders from the prison-based Mexican Mafia, was sentenced Monday to nearly 20 years in prison. His son, Louis Rios, 22, got 10 years.

They had pleaded guilty to conspiring to attack black people in a campaign to push them out of the city some 25 miles east of downtown Los Angeles.

The father and son were among 49 others suspected of being Azusa gang members and arrested in 2011 on charges they conspired to target and harass black residents for a decade. All the defendants have been convicted, and eight are still awaiting sentencing.

"The sentencing of the gang's 'key holder' is another giant step forward for the residents of an area who lived for too long under the specter of gang violence and racial animosity," U.S. Attorney Andre Birotte Jr. said in a statement.

Rios told investigators the gang's goal was to make black people leave Azusa. He also said he and other members of the gang intimidated and attacked blacks at their homes, on the streets, at convenience stores and elsewhere because of their race.

The gang also scrawled graffiti containing racial slurs on walls and buildings to intimidate black people, and new gang members participated in attacks as part of an initiation ritual, authorities said.

"The investigation and today's sentencings send a loud and clear message that hate and gang crimes will not be tolerated, and will be prosecuted to the fullest extent of the law," Azusa police Chief Sam Gonzalez said in a statement.

Gang members were also accused of conspiring to distribute heroin, methamphetamine and cocaine through a business plan that outlined methods to control the narcotics trade in the city, according to court documents.

The gang extorted payments from street-level drug dealers in exchange for doing business in Azusa, authorities said.