Originally Ashfall was set in Indianapolis, where I live. (Write what you know, right?) Alex fled from Indianapolis toward a farm in Yellow Springs, Ohio, modeled on my brother’s farm. But as I researched the Yellowstone supervolcano, I quickly realized that the disaster wouldn’t be bad enough in Indianapolis. It would be horrible everywhere, as food supplies ran out and mass starvation ensued, but I wanted to write about ash, lightning, and collapsing buildings–not slow death by starvation. Based on maps of the Yellowstone super-eruption of 2.1 million years ago, I estimated that the closest Alex could start to a similar eruption and have a realistic hope of surviving would be about 900 miles. I got out an old Rand-McNally road atlas and drew a circle around Yellowstone 900 miles in radius. That circle neatly bisected Waterloo, Iowa.

Later, my wife and I traveled to Iowa. I wanted to fill in details of the story and get the road names and neighborhoods right. We drove every mile that Alex walks or skis through Iowa and Illinois. In Waterloo, we searched for Alex’s house. I needed it to be an older neighborhood with two-story homes. It also had to be hip enough that Joe and Darren could live across the street. After several hours of roaming more or less randomly, we found the perfect house for Alex in Cedar Falls, just across the river from Waterloo. Alex, and the start of Ashfall, moved to Cedar Falls, Iowa.