Which was identified as the border between u. s.-owned and british-owned land in 1846?

49th parallel.

Explanation:

Through the Treaty of Oregon (June 15, 1846) Britain and the United States established the 49th parallel as the main international border in the Pacific Northwest. This treaty settled the conflict with Britain over the Oregon territory. The United States obtained legal authority over what would later become the states of Oregon, Washington, Idaho, and Montana, while the British held Vancouver Island and part of the Columbia River.