Hammered by wind, a mossy ghost tree haunted the hillside above Squaw Creek canyon, which lay just beyond the ledge, 200 feet below. I looked over the edge and wanted to leap into it, beckoned by all that space. I had the same feeling a few months ago at Dia:Beacon, peering into Michael Heizer's North, East, South, West installation. There is something about emptiness that makes you want to fall into it. And there is something about mountains that makes you want to stand back and stare. Mountains push you back, but canyons pull you closer. Mountains and canyons — nature's two-part tutorial on the different species of Wow.