If you are normal-weight or more and have no medical issues you can not eat anything at all for a week and still be fine (although pretty grumbly and dreaming about food), so yes. You can eat oatmeal and nothing else for a week. Why you'd do that is beyond me, but you can.
Yellowstone County is the most populous county in the U.S. state of Montana. As of the 2010 census, the population was 147,972, and a 2014 estimate put the population at 155,634. Its county seat is Billings. Yellowstone County is named for the Yellowstone River which roughly bisects the county from southwest to northeast. The river in turn was named after the yellow Sandstone cliffs in what is now Yellowstone County. Yellowstone County is included in the Billings, MT Metropolitan Statistical Area.
Yellowstone Avenue in winter. West Yellowstone is a town in Gallatin County, Montana, adjacent to Yellowstone National Park. The population was 1,271 at the 2010 census. The town is served by Yellowstone Airport. It is part of the Bozeman, MT Micropolitan Statistical Area.