Keystone Mapping Project: Oil Spill Voluntary Evacuation Zone. Milepost 042. Montana. Published July 5, 2012 at 1000 × 589 in Keystone Mapping Project: Oil Spill Voluntary Evacuation Zone. Milepost 042. Montana. Two-mile Voluntary Evacuation Zone.; Proposed Keystone XL route.; Milepost 042. Montana.