Sunday the 13th is a totally unorganized effort of individuals wanting to help bring attention to the 'Clean up'.
On the 20th I suspect that there will be many more in attendance due to the attention via the 13th Clean Up (and you know you can always count on the U.S. Government to help bring attention to people cleaning a park).
This is not new to Arizona. During the last major "shutdown" in the mid 90's Arizona's then governor, Fife Symington, used State Guard, State employees and donations to keep the Grand Canyon open. He was then targeted in court, forced to resign and then eventually given a Presidential Pardon by Bill Clinton. So I wouldn't count on any "Shiny Badgers" to help.