George Riggs, former publisher of the Mercury News and Contra Costa Times, announced today he is stepping down from his post as top executive of California Newspapers Partnership, the three-company group controlled by MediaNews that owns most of the Bay Area’s daily papers.

According to a report in the Merc, Riggs, 61, said he left of his own accord from the position he had held for 18 months. Riggs’ resignation comes 11 days after Merc editor Carole Leigh Hutton resigned and was replaced by MediaNews vice president David Butler. She too said she left on her own — less after a month when she proposed reducing the Merc to a three-section paper.

Media News chief executive Dean Singleton said that Riggs’ responsibilities will be assumed by Steve Rossi (right), MediaNews executive vice president and chief operating officer. Rossi is familiar with the Merc and CC Times from his days as head of Knight Ridder’s newspaper division, which owned those papers for many years. Rossi was long seen as the heir apparent to Knight Ridder chairman Tony Ridder.

The California Newspapers Partnership includes 33 daily newspapers with a combined circulation of more than 1.2 million and generate about $1 billion in annual revenue, according to MediaNews. The papers include the Merc, CC Times, Oakland Tribune, Marin Independent Journal and many in the Los Angeles area. MediaNews owns 54.2 percent of the partnership while the rest is held by Gannett Co. and S.F. Holding Corp., formerly known as the Stephens Media Group.