There was significantly more in the area you ask about 5-10 years ago.
A large number of such locations are being shut down.
One of the big reasons is the significant amount of trash left behind.
Of those that remain it is often because of volunteer groups that "adopt" the location and go pick up several large truckloads of trash annually.
However even then the trucks that transport the waste are often paid for by government or forestry services, in a state that has a government that is already not particularly fond of firearms.
The volunteers make it significantly cheaper to clean these places up, but typically not free.
So these places still exist, but they are rapidly diminishing in numbers even in remote areas.
If you go please take more trash with you than you brought.