After having a record-setting year in 2015, Washington, Colorado and Oregon have set the bar extremely high in legal weed sales. Over the course of 2015, sales took 17 percent jump for a total haul of $5.4 billion, placing projections for 2016 in the ballpark of $6.7 billion. However, according to an ArcView Market Research, the next four years could result in a dramatic shift in the already booming industry, which is expected to rake in $21.8 billion by 2020. Read more below.