The path less trodden to adventures in fall written by James Sinks Fittingly, for a movie about off-duty Halloween monsters, Disney producers scouted for a ghost town. They found a perfect backdrop in northwest Oregon’s St. Helens. The mills were long gone, but the once-busy downtown boasted a picturesque public square, a classic courthouse and a stunning view of its namesake, Mount St. Helens, 39 miles away across the Columbia. Filmed a quarter century ago, Halloweentown became a cult classic and even spawned several sequels. Soon after, cameras returned for the vampire-teen romance mashup Twilight, in which St. Helens stood in for another timber town, Forks, Washington. Now, each autumn when Mother Nature readies her technicolor picture show, St. Helens unpacks the nostalgia, costumes and cash registers. For six weeks, downtown and the central plaza—where usually you can trace Lewis and Clark’s voyage on stepping stones—are transformed into the “Spirit…