The bill’s author, State Senator Anthony Portantino, a Democrat, said he was “cautiously optimistic” that the law would withstand the legal challenges. “Clearly, Californians will be safer when S.B. 2 becomes law,” he said, adding that the restrictions are “in the best interest of the public.”

Along with banning the carrying of guns in most public places, the law sets the minimum age for obtaining a gun license at 21 and adds more requirements for gun safety training before receiving a new license.

The public places covered by the law are divided into 26 categories with various locations, including playgrounds, public transportation, stadiums, amusement parks and museums. The law also prohibits people from carrying firearms on the grounds of private businesses unless there is clear signage indicating that they are allowed.

Concealed carry permit holders and other gun-rights organizations, including California Rifle & Pistol Association, the Second Amendment Foundation and the Gun Owners Foundation, filed a challenge against the provisions banning guns from certain public places.

But the California attorney general, Rob Bonta, who appealed Judge Carney’s decision, argued in a statement that “guns in sensitive public places do not make our communities safer, but rather the opposite. More guns in more sensitive places makes the public less safe; the data supports it.”

C.D. Michel, general counsel for California Rifle & Pistol Association, said the Saturday ruling from the appeals court was “not really a win” for the state yet, since the court still must judge on the merits of the case.

“For decades, people with a license to carry in public have been able to carry in all of these places,” he said.

He called the state law an “effort to get around Bruen,” referring to the U.S. Supreme Court ruling in a case, New York State Rifle and Pistol Association v. Bruen, that struck down a New York law that had strictly limited the carrying of guns outside homes. The Supreme Court dramatically shifted the standard for restrictions on firearms with that decision in 2022.

Since then, several states have moved to restrict the carrying of firearms. New York, for instance, passed a law to prevent people from carrying guns in “sensitive locations” such as Times Square, public transit, sports venues and houses of worship. The law has created confusion and generated numerous lawsuits.

Illinois also banned high-powered guns this year, in response to a mass shooting on July 4, 2022, in Highland Park, a Chicago suburb. This month, the U.S. Court of Appeals for the Seventh Circuit, based in Chicago, upheld that ban.

When Mr. Newsom signed the ban on guns in public places into law, he also approved a sweeping series of gun safety measures, including the microstamping of handgun cartridges to help with tracing crimes and an effort to use funds from bullet sales to improve gun violence intervention programs and school safety.