The number 420 has been associated with marijuana use for decades, though the reasons are murky. Its use as code for marijuana spread among California pot users in the 1960s and spread nationwide among followers of the Grateful Dead.
Theories abound on its origin. Some say it was once police code in Southern California to denote marijuana use, probably an urban legend. It was a title number for a 2003 California bill about medical marijuana, an irony fully intended.
Others trace it to a group of California teenagers who would meet at 4:20 p.m. to search for weed, a theory as elusive as the outdoor cannabis crop they were seeking. The code stuck because authorities and nosy parents didn't know what it meant, at least for a while.
In Colorado, recent 4/20 observations blossomed alongside the state's medical marijuana industry. Approved by Colorado voters in 2000, medical marijuana boomed after federal authorities signaled in 2009 they would pursue higher-level drug crimes. All marijuana is illegal under federal law, though Colorado voters this November will consider whether to legalize it for recreational use for adults over 21.
At the University of Colorado, three students were arrested for trespassing when they walked onto the Norlin Quad, sat down and refused to leave, campus police said. Eleven others, including two students, were ticketed for trespassing, and one was ticketed for marijuana possession on campus, police said.
One of the three arrested told reporters the crackdown was more disruptive than any of the previous years' rallies.
Campus police spokesman Ryan Huff estimated the university would spend about $110,000 on law-enforcement Friday, about double the amount spent last year.
The yellow tape was removed from the quad and officers began withdrawing shortly after 4:20 p.m.
Playboy magazine named Colorado the nation's top party school in 2011. The campus also repeatedly ranks among the top schools for marijuana use, according to a "Reefer Madness" list conducted by The Princeton Review.
The University of Colorado's student government supported the university's anti-4/20 actions. And other Colorado students created a Facebook campaign urging their colleagues to wear formal clothing to school on Friday to repudiate the party-school reputation.
Associated Press writers Kristen Wyatt, P. Solomon Banda and Thomas Peipert contributed to this report.
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