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The university does not sanction the so-called event, and this year the school said it was doing more to crackdown on participants.
Officials are limiting access to the campus and have instituted a no guest policy in student dorms.
4/20 is known among pot smokers world wide as code for the "time to get high."
Many believe it originated at San Rafael high school in 1971 by a group of kids who needed a code so they could talk about smoking weed, secretly, around parents and teachers.
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