What do you call this stuff? (2019–)

Growing up, my friends and I played on the school playground every day. It had pieces of wood on the floor, which we called "tanbark." Recently, I learned that no one outside of the San Francisco Bay Area knows this word. For the rest of the English-speaking world, the material is apparently "woodchips," "mulch," or something else.

 

I decided to make a survey, and I received more than a thousand responses. The findings were interesting. Hundreds of people in the Bay Area say “tanbark,” but hardly anyone else. The area around Ohio says “mulch” a lot. And many people in the Northwest just say "bark."

 

I learned that there's a tree called “tanbark oak” native to Northern California, so maybe that's where it originated/ But why has the word "tanbark" stayed so prominent there? Why didn't it spread past NorCal or go extinct at the hand of the more mainstream words? My theory is that the only speakers of the word "tanbark" are kids. Kids don't move between different cities as much, they don't talk to many other kids in faraway places, and they stop talking about playground equipment when they turn ten. "Tanbark" is a view of the world through the eyes of the child: a huge and impenetrable place. The child's world is the world before maps, in which you only know your own corner of the world, and everything beyond is a mystery.

Please take the survey! And here's the link to the map.