Regardless who leaves it, it will stay there or wash away unless some one picks it up or the wrong thing makes a meal of it!
So you can be pissed and point blame or simply pick up 1 piece on your way out and deposit it in a receptical to be put in a beautiful canyon landfill on land that once might have home to some native fish, birds, reptiles, or bugs!
Lets face the facts that we are all destructive to mother nature regardless of our habits!
Question is how do we fix it!