The environmentalists want to close 446,760 acres of public land to target shooters when the BLM says it is OK. Until 2015 you could target shoot on all 496,400 acres but because of environmentalist complaints the BLM reconsidered and restricted almost 50,000 acres now those environmentalists are still not happy because they want to close the entire area. Just like gun grabbers will never be happy until all guns are banned the environmentalists want all shooting banned.
Map showing the Sonoran Desert National Monument and the closed areas.
https://luke.isportsman.net/files/maps/SDNM_17x23_2016.pdf
The trouble is some people just CANNOT STAND to have others enjoying themselves. They take it as a Divine Charter to forbid as much as they can until everything is forbidden. Then they move on to a different location to start all over again.