The three US states that extend west longitude 120 degrees are Oregon, Washington and California.
Oregon: it is a state in the Pacific Northwest region on the West coast of the United States.
Washington: it is also a state in the Pacific Northwest region of the United States. The name of the State was after George Washington who was the first President of the United States.
California: it is the most populous and western state in the United States, it is the third most widespread state by area.