DENVER—The counterculture marijuana holiday known as 4/20 is getting an early start in Denver, where tens of thousands are expected for a group smoke-out on the first celebration since Colorado and Washington made pot legal for recreation use.

Reggae music filled the air, and so did the smell of marijuana, as celebrants gathered by mid-morning in a park just beside the state Capitol. Few police were in sight, though public marijuana use is still prohibited here.

Organizers say the Denver event could drawg a record 80,000 attendees this year.

Authorities generally look the other way at public pot smoking here on April 20. Police said this week they’re focused on crowd security in light of attacks that killed three at the finish line of the Boston Marathon.