This seems to be the rule now at all USFS shooting areas. I noticed when we went to Harris Park in September there were signs everywhere saying no plastic bottles, glass (duh!), metal cans, etc.
When I rode out to Pawnee Buttes I saw the same thing on a big sign: Manufactured targets only, no plastic, etc.
We like to fill plastic bottles with water and shoot them but apparently that's now verboten. We are always careful to pack out our trash (and more) but of course, somebody's gotta ruin it for everybody. Honestly after seeing the trash heap at the Rampart Range facility, I can kind of understand it.
I assume clays are still OK (I think the rules specifically say they are.) Maybe find a way to hang some clays off of a metal target stand and shoot at those. Not as much fun as watching a water-filled jug blow up though.