The Denver Post -It was a warmer-than-average, sunny day in Boulder on Sunday.
And around 4:20 p.m. on the University of Colorado campus, the sky grew unusually hazy.
Cheers erupted along with a heavy cloud of smoke as an estimated 10,000 people - mostly CU students joined by friends from out of town and some local residents - lit up to celebrate at an annual pot-smoking rally.
Some said they were there to advocate for the legalization of marijuana. Others - including some who came just to watch - said it was all for fun.
"It's like, why do people drink beer on St. Patrick's Day?" said a 22-year-old "super senior" who didn't want to give his name. "It's a holiday. Like the Fourth of July."
The number 420 is slang for marijuana. Across the country each year, pro-pot rallies are held on April 20 or 4/20.
Though there were events all day long on the CU campus, from an art display to live bands, the students chose 4:20 p.m. for the massive smoke-up at Norlin Quadrangle.
A few guys played drums. Some girls danced. Beach balls and Frisbees flew through the air.
CU police monitored the gathering, with 15 campus officers and six Boulder County sheriff's deputies stationed around the perimeter and directing traffic.
According to a news release, the focus was to "maintain a safe environment and discourage potentially hazardous activities."
No citations were issued and there were no arrests, although there were four medical incidents and two people were transported to local hospitals, the release stated. One person was treated for a seizure, the other for dehydration.
The Rocky Mountain News