Yes. Of course. They can fire you for consuming alcohol if they want, or even smoking cigarettes. They can fire you for liking the 49ers. They can fire you because they feel like it. They can't fire you because of: race, gender, sexual orientation, or religion. 

Oh ya, it's just less likely if its legal, even in other states most people that get caught dont get terminated 

Hey r/trees. Question: Can a corporation in Colorado or Washington fire a potential employee solely on the basis of them consuming/smoking marijuana?