The Puente Hills Landfill, one of the nation's largest, is about to fill up and shut down. Where will all the garbage go then? Why do we waste so much? Can we stop? What about recycling, which was a big political issue at one time in Los Angeles? The late Mayor Sam Yorty promised voters they would not have to sort one kind of trash from another. Now, of course, the cans are green and black and blue as we all dutifully participate in recycling all over California.