The Snake River and the Idaho line in Ontario
Ontario is a border city. Wikipedia says it sits on the Idaho state line and is the closest city to the Idaho border along Interstate 84, with the Snake River forming its eastern boundary and the state line.
Mountain Time
Ontario observes Mountain Time, UTC-7, with Mountain Daylight Time in summer, according to Wikipedia. Most of Malheur County is on Mountain Time, and the southern fifth is on Pacific Time. Wikipedia reports that local time changed to match train time after an Interstate Commerce Commission order dated May 13, 1923. If you plan around Ontario, remember that it is an hour ahead of most of Oregon.
Across the river
Wikipedia notes that Payette County, Idaho is part of the Ontario micropolitan area.