You're asking about the 48th parallel North. There are more than 3 US states that lie along this line, but here are 3 prominent ones:

* Oregon: The northernmost point of Oregon sits at 46.15° N, while the southernmost point of the state is at 42.01° N. This means the 48th parallel cuts through the state.

* Idaho: The northern border of Idaho sits at 49.0° N, while the southern border is at 42.0° N. The 48th parallel slices through the northern portion of the state.

* Montana: The northernmost part of Montana is at 49.0° N, while the southern border is at 44.5° N. Similar to Idaho, the 48th parallel intersects the northern region of Montana.