Nestled in the scenic Yellowstone River valley along the Montana-Wyoming border, Gardiner, Montana — with its Old West facades, fly shops, and whitewater outfitters — serves as a year-round gateway to Yellowstone National Park. Its proximity to the northern entrance to the country’s oldest and arguably grandest national park fuels the town’s tourism-based economy. With a year-round population of fewer than 900 people, Gardiner is almost entirely reliant on the nearly three-quarters of a million visitors who pass through Yellowstone’s north gate each year. The summer season, the busiest and most lucrative time of year for most Gardiner businesses, was just getting into full swing this month. Seasonal workers from around the country were settling into their summer jobs. Hotels were filling up. Rafting trips were underway. Tourists were pouring in. On Monday, everything came to a screeching halt.