Oregon was able to legalize marijuana by getting the community to rally and let the people in positions of power realize how important this was to them. A strong community base can get things done and this is what you saw in Oregon was able to legalize medical marijuana.
In 2014, Oregon legalized marijuana through Oregon Ballot Measure 91. On July 1, 2015, it became legal for adults age 21 and older to possess, use, and cultivate marijuana for non-medical purposes. Recreational marijuana became available for sale through existing medical marijuana dispensaries on October 1, 2015, and applications for retail sales licensed by the Oregon Liquor Control Commission became available on January 4, 2016.
A bill, called Measure 91 was introduced onto the ballot that would enable it to be legal for anyone over 21 to use and sale of recreational marijuana. In the 2014 election, the bill was voted on. It was approved by 54%, and was implemented Effective July 1, 2015. The bill has measures to study the effects of legalization both financially and socially.