Final answer:
The Blue Mountains form the eastern border of Oregon.
Step-by-step explanation:
The natural features that form the eastern border of the state of Oregon in the United States are the Blue Mountains.
The Blue Mountains, also known as the Wallowa Mountains, are a mountain range in northeastern Oregon. They form part of the border between Oregon and Idaho.
The Blue Mountains provide a scenic backdrop to the eastern region of Oregon and are home to diverse wildlife and recreational opportunities.
Learn more about The Blue Mountains