On its long-distance journey across the continent, Interstate 70 traverses 449.6 miles through Colorado. Its east-west trip is marked by hundreds of mileposts, which count upward beginning with the zero mile marker at the western border with Utah.

The first few hundred mileposts always seem to fly by as drivers bask in the scenery of Glenwood Canyon and the grandeur of the snow-capped Rockies. East of Denver, however, the markers seem to tick away much more slowly as the interstate begins to cross the flat prairie.

Between the towns of Watkins and Bennett, drivers pass milepost 300. Agate (population 518) is located at mile marker 340. By milepost 400, east of Flagler, most drivers have completely tuned out. Just past Stratton (population 664), however, it’s worth paying attention to see one of Colorado’s quirkier sites: Milepost 419.99.

CDOT installed this unusual marker in 2014 after thieving stoners repeatedly stole the standard “420” sign. (420 is, of course, a code for the “time to get high” or “time to smoke pot,” and April 20 is known as the day to celebrate and smoke cannabis”—preferably at 4:20 p.m.)

The origin of this term remains a bit hazy; rumors—no doubt sparked during long smoke-a-thons—include that it commemorates Bob Marley’s death or Adolf Hitler’s birthday, or that it refers to the number of chemicals in weed. More likely, however, is the explanation offered by Wikipedia, which attributes the term to a group of high schoolers from San Rafael, California, who called themselves “the Waldos” and started using the magic numbers as a code for their illicit activities while at school.

Regardless of the term’s origin, many pot smokers have taken the term to heart, and April 20 has become a nationally celebrated day, especially in 420-friendly Colorado. Since I-70 is one of just a few highways in the state that’s long enough to have a 420 marker, pilfering potheads repeatedly targeted its iconic sign, forcing CDOT to come up with this, er, unique solution that Dewey Decimal himself would be proud of.

Visit: This unique milepost is located on I-70 in eastern Colorado, about 25 miles from the border with Kansas. Much closer to home, however, is Downtown Denver’s 420 Festival, which will be celebrated on Saturday, April 16.


Terri Cook
Terri Cook
Terri Cook is an award-winning freelance writer based in Boulder. More of her work can be found at down2earthscience.com.