Monday's ruling is the latest, and not likely the last, in an ongoing attempt by the gun lobby to break the state's prohibition on certain types of firearms.
The Los Angeles Times reports that the ruling that was put on hold was made several weeks ago by Judge Roger T Benitez, who likened AR-15s to Swiss Army Knifes, calling them "good for both home and battle”.
Under that ruling, the state had 30 days to appeal, which was all but guaranteed to happen. Under the new order, the changed gun laws cannot come into effect until pending gun cases in court have been resolved.
“This leaves our assault weapons laws in effect while appellate proceedings continue,” Attorney General Rob Bonta said in a tweet. “We won’t stop defending these life-saving laws.”
The 9th Circuit is adjudicating another case challenging the state's assault weapons prohibition, but it is also on hold until another ruling is made regarding the state's ban on large-capacity magazines.
Governor Gavin Newsom lashed out at Mr Benitez for trying to dismantle the state's assault weapon ban, calling him a "wholly-owned subsidiary of the gun lobby and the National Rifle Association" and a "stone-cold ideologue”.
Mr Benitez also was responsible for blocking legislation in 2016 that would ban large-capacity magazines. The state fought him and eventually won.
"We need to call this federal judge out," Mr Newsom said. "He will continue to do damage. Mark my words."
The judge was appointed under George W Bush and is based in San Diego. He has ruled on several weapons cases, including a pair in 2019 and 2020 dealing with ammunition restrictions.
Mr Newsom claims that gun rights activists and the gun lobby try to have firearms-related cases heard by the judge in a move he called "judge shopping”.
California is one of seven states that bans assault weapons.
It is likely the case will end up in the Supreme Court.
Twenty-two states, led by neighbouring Arizona, joined together to petition the appeals court to support Mr Benitez's ruling.
The states claimed that most rifles were for completely legal reasons.
"Calling modern rifles 'assault weapons' is a misnomer – they are most often used by law-abiding citizens for lawful purposes like personal protection or target and sport shooting," the coalition of states argued. "There is nothing sinister about citizens keeping or bearing a modern rifle."
While it is true that gun crimes generally tend to involve pistols, not assault rifles, it still remains that the US' deadliest shooting – the 2017 Mandalay Bay mass shooting in Las Vegas – involved a shooter using AR-15 "modern rifles" with attached bump stocks to kill 60 people and injure 411.
The states that opposed California were Alabama, Alaska, Arizona, Arkansas, Georgia, Idaho, Indiana, Kansas, Kentucky, Louisiana, Mississippi, Missouri, Montana, Nebraska, Ohio, Oklahoma, South Carolina, Tennessee, Texas, Utah, West Virginia and Wyoming.
All of the challenging states are led by Republican state legislatures. Republicans have traditionally argued that the federal government should allow states to largely rule themselves and not butt into their affairs. That ideology also traditionally crumbles any time it is convenient for conservative lawmakers to call for federal intervention.