As of the first of the year, anyone over the age of 21 in California is legally allowed to consume cannabis at licensed businesses as well as private properties. But one California staple has completely and officially banned marijuana on its grounds.
The official website explains, "Sorry bro. Marijuana and marijuana products aren't allowed inside Coachella. Even in 2018 and beyond. If that changes, we'll update this answer."
With cannabis laws changing and growing right now in California, this doesn't come as much of a surprise. It seems that Coachella is treading lightly with all the new regulations surrounding marijuana and aren't jumping the gun in stating that it's a safe space for use.
Alas, if concertgoers happen to "forget" that cannabis isn't allowed, they will be provided an "amnesty box" to store their marijuana at no consequence.