In U.S. v. Gray, a June 26, 2019 unpublished opinion of the 9th Circuit, the court held that a Reno, Nevada search was legal when the officers smelled the odor of marijuana and conducted a search resulting in discovering a firearm in possession of the felon defendant.   Because possession of less than one-ounce of marijuana is legal in Nevada, the defendant argued the odor of marijuana did not justify a search. 

The court disagreed, noting it is still an infraction in Nevada to smoke or consume marijuana in a public place or in a moving vehicle.  The officer reasonably believed the defendant was lying and could infer this indicated a guilty mind.   Once the drug dog alerted for contraband, the officers were justified in their belief that evidence of a crime was present. 

The opinion is here:US v Gray Unpub MJ odor 18-10190.pdf

In Washington, the odor of marijuana would also justify reasonable suspicion for an infraction and possible DUI impairment, but a search warrant would be needed after seizing the vehicle to search absent either consent or an exigent circumstance.