DENVER — A Colorado law that allows adults to legally possess and use marijuana may now allow some people found guilty of minor marijuana crimes to challenge their convictions in court, a state appeals court ruled on Thursday.

The decision by the Colorado Court of Appeals stemmed from a 2010 drug case in which a woman from the mountains west of Denver was convicted of possessing small amounts of marijuana and a concentrated form of the drug — both of which are now legal under a 2012 ballot measure approved by Colorado voters. Her lawyers argued that the legal landscape had shifted since she was charged and that her marijuana convictions should thus be thrown out.

The court agreed, saying that the legalization law, known as Amendment 64, could apply retroactively to minor drug offenses if people had already been appealing their convictions when the measure went into effect.

Marijuana advocates cheered the decision, calling it a sign that growing public support for legalizing or decriminalizing marijuana was beginning to resonate in legal circles. They said it could help dozens of people to successfully overturn convictions for possessing less than an ounce of marijuana concentrate or for growing six or fewer marijuana plants in their homes — acts that were once illegal, but that are now allowed for adults 21 and over.