Gwynne Ann Unruh is an award-winning reporter formerly of the Alamosa Valley Courier, an independent paper in southern Colorado. She covers the environment for The Paper.

There’s gonna be a party around the state this year on 4/20 whether you are sequestered at home or not. It’s been a Hard Day’s Night getting ganja legalized in New Mexico, and it’s appropriate that pot became legal in April, as this month holds the celebration day honoring cannabis around the world. The term 420 will be on the mouths of many New Mexicans in the cannabis culture who imbibe as they celebrate the legalization of recreational cannabis in their enchanted land this year. The international counterculture holiday 4/20 at 4:20pm is when marijuana enthusiasts around the world light up a joint in celebration of cannabis.

The dayis beloved by pot smokers around the world as a reason to toke up with friends each year. The numerical code for marijuana—420, 4:20, or 4/20 is “Weed Day,” and in the cannabis culture it’s used as slang for marijuana and hashish consumption, especially smoking around the time 4:20pm on April 20. In the United States on 4/20, tens of thousands of Americans traditionally gather around the country for cannabis-oriented celebrations for a drug that remains illegal in the U.S. federally—while states around the country are just saying, “No” in rapid succession and legalizing cannabis within their state, both for medicinal and recreational use. 

So how did the date become an international holiday for smoking and celebrating the green weed? The most plausible story comes from Chris Conrad, curator of the Oaksterdam Cannabis Museum in Oakland, California. The secret code “4:20” was originally used by a group of friends at the San Rafael High School in California in the early 1970s who called themselves “the Waldos” and participated in ritually smoking marijuana every day at precisely 4:20pm, getting high in front of a statue of scientist Louis Pasteur.

In 1971 the five high school students used the term “4:20” as a code name in connection with a plan to search for an abandoned cannabis crop, based on a treasure map made by the grower. One of the Waldos would call for a “4:20 Louis” which meant that everyone was to meet at the statue to search for the marijuana on the treasure map.

Eventually “4:20 Louis” became just “4:20,” and the number became recognized not as a call to hunt for the abandoned cannabis, but as a code word for saying, “Let’s go smoke some pot.” True potheads are supposed to smoke every day at 4:20pm and all day on April 20. As the 420 ritual spread, it was converted into 4/20 for calendar purposes, birthing the day of celebration. This ultimately led to 420 being the code for anything marijuana related.

Interestingly, California Senate Bill 420 (known as the Medical Marijuana Program Act) was a bill introduced by John Vasconcellos of the California State Senate, and it subsequently passed by the California State Legislature and was signed by Governor Gray Davis in 2003.

Generally, when you see the term 420-friendly in website advertising for housemates, tenants or in dating app advertisements, it simply means that the person or place is accepting of people who smoke weed, or is open to dating someone that uses marijuana and probably does themselves. Some say “420” is code among police officers for “marijuana smoking in progress.”

Many hotels have removed the number 420 because of its links with the cannabis culture. The number is an attraction for pot smokers. One hotel has taken to indicating its room 420 with a sign that reads 419+1 in a bid to avoid links with marijuana.

When recreational use of marijuana was made legal in Colorado in 2012, the “Mile Marker 420” post became highly coveted, and zealous, giggling, sticky fingered marijuana enthusiasts kept stealing the highway marker located on a stretch of Interstate 70 just west of the Kansas border. “Obviously people steal these signs,” Amy Ford of the Colorado Department of Transportation told the Denver Post. “In the past, if a sign was stolen too much, we wouldn’t replace it.”

When the Colorado Department of Transportation really got tired of replacing the marker, they got creative and transportation officials found a way to foil the thieving potheads. They removed the “420” mile marker along Interstate 70 and replaced it with “419.99.” “This is sort of an innovative way for us to keep the sign there,” Ford said.

The mile marker spot had become a destination—for some it was just to see if the sign was for real, for others they went there to grab a few selfies with a joint in hand. While there was less sign thievery than before the switch, it hasn’t been a complete success. The Mile 419.99 sign went missing a few times too. So now it appears to be permanently closed. 

Another holiday for cannabis use has recently come onto the cannabis scene: July 10. The number 710, or 7/10, is now also considered a “stoner” holiday for consuming cannabis oil products or concentrates. The term 710 rotated upside-down spells OIL, a word used to describe highly potent cannabis products such as hash oil, shatter, wax, etc.

If you are looking for a historical road trip across the U.S. this summer, the following states have 420-mile markers: I-5 California, I-10 Texas, I-20 Texas, I-35 Texas, I-40 Tennessee, I-40 North Carolina, I-70 Colorado (maybe), I-70 Kansas, I-75 Florida, I-80 Nebraska, I-90 Montana. In New Mexico, Interstate 10’s length is 164.3 miles—not a problem. Interstate 25 is 462.124 miles long within the state. That marker is an endangered species. Start your engines.