There’s a full moon over Hoover Dam, and we drive across in the dark from Nevada to Arizona and park. We walk back across even though no one is supposed to be on the dam after sunset. Nobody stops us or says anything. I’m in awe of this giant slide of concrete, built in layers and still curing, drying, strengthening even after more than 80 years. Smooth and pale next to the dark crags rising on either side to flank the Colorado River, the dam drops into shadow at the bottom. It seems almost like a living thing, massive and eerie, asleep. I lean over and tremble at what it would be like to fall silently down into its mouth. If I got too close, sat on the thick edge, what would stop me from slipping over? Why is it we humans think like that–find the fear, imagine the bizarre chance of circumstance, the tragic trajectory? To push back the edge of terror, like the dam pushes back the flood waters, I kiss my husband since it’s the top of Hoover Dam on a warm September night. But the creeping fear seeps through my dam and follows me out through the shadows looming and shrinking as we pass the watchful street lamps.