I-84 between 370 and 355.
There are three pretty big hills about 10 miles NW of Ontario. They like to hang out there where a motorist might get up a little too much speed on the downhill side(s).
Note: Please check your reference mile markers on I-84. Baker City is at 305, Ontario, the east state line, is at 377, and it starts at 0 somewhere at or near Portland. The reversal of the mile markers may be confusing to motorists not familiar with the area.