Boulder banned assault weapons in 2018. A judge recently ruled that the city cannot enforce the ban.

In 2018, the city of Boulder, Colorado, passed a ban on the sale and possession of assault weapons and large capacity magazines. Earlier this month, a state district court judge blocked the city from enforcing its ban.

source https://www.cnn.com/2021/03/23/politics/boulder-assault-weapons-ban-trnd/index.html