<P> Time in Oregon is divided into two zones . The vast majority of the state is contained in the Pacific Time Zone . Most of sparsely populated Malheur County, including its largest city, Ontario, and its county seat, Vale, are in the Mountain Time Zone due to their proximity to Boise, Idaho . The time zone division occurs at the southwest corner of township 35 S, range 37 E (approximately 42.45 degrees north latitude), continuing east to the state line, then south along the Oregon - Idaho border to the Nevada state line . </P> <P> Drewsey in Harney County is officially in the Pacific Time Zone, but some residents unofficially observe Mountain Time due to proximity to Malheur County . Local businesses and the Oregon Department of Transportation strictly enforce the practice of Pacific Time, however . </P>

Why is part of oregon in mountain time