A plea to nature writers: Come write about Los Angeles. To all the young aspiring Thoreaus out there: Head to this megalopolis in droves, as if to Mecca. Chicago is also good. New York. Pittsburgh. Atlanta. Reno. Providence. Houston. Indianapolis. Who needs the woods? Photo: iStockphoto Why does the venerable American literary genre of nature writing continue to ignore cities? Sure, a few wonderful writers are traveling the mean streets: very recently, Michael Pollan has rooted urgently through our supermarkets and kitchens. But when I browse the state-of-the-genre bible, the 2002 Norton anthology of nature writing, I can find only …