A marijuana plant grows at the Colorado Harvest Company in Denver, Colo. on Wednesday, July 8, 2015.

(Nathaniel Minor/CPR News)

Colorado pot stores sold a record amount of marijuana in June, a huge leap over the previous record set in March. What's not clear though, is why.

Recreational marijuana sales topped $50 million in June for the first time. Medical marijuana also had its biggest month in more than a year.

Some stores owners speculated that business was driven by the summer weather, lower prices and the expansion of stores into Aurora. Some owners there reported seeing more than 300 customers a day.

At the halfway mark of 2015, Colorado stores have sold nearly half a billion dollars in marijuana and paid about $60 million in taxes to the state.