The highway that became US 730 within Oregon has been designated by the
Oregon State Highway Commission as the easternmost segment of Columbia River Highway No. 2 since November 27, 1917, created as part of the initial
named state highway system. The segment of US 730 within Washington was added to the
state highway system in 1923 as a branch of
State Road 3 and kept its designation as a branch of
PSH 3 during the creation of the
primary and secondary highway system in 1937. The United States Numbered Highway System was adopted on November 11, 1926, by the
American Association of State Highway Officials (AASHO) and included US 730, traveling northeast along the Columbia River from US 30 in Umatilla to
US 410 south of Wallula. The highway was originally planned to be numbered as US 420, but was changed after US 30 was substituted in place of
US 20 along the Columbia River. US 395 was extended south from
Spokane, Washington, to
San Diego, California, in 1937, becoming concurrent with US 730 between Cold Springs Junction and its eastern terminus at US 410 south of Wallula. US 30 was moved to a new section of the
Old Oregon Trail Highway No. 6, bypassing the cities of Irrigon and Umatilla, on November 25, 1946. US 730 was subsequently extended west to a new junction with US 30 and later relocated uphill due to the construction of the
John Day Dam. The highway's western terminus was moved farther south to an interchange with
I-80N in 1967. During the westward extension of US 12 from
Idaho into Washington, the Oregon state government suggested to AASHO a route that included the entirety of US 730 in 1962, while Washington state suggested routing US 12 over US 410 and
State Route 12 (SR 12) to
Vancouver, Washington. AASHO approved the extension of US 12 into Washington on June 20, 1967, routing it along US 410 and
SR 14 to its present terminus in
Aberdeen. US 395 was re-aligned to a concurrency with I-82 in 1985, crossing the Columbia River on the Umatilla Bridge and having a shorter concurrency with US 730. The old route of US 395 from Cold Springs Junction to Pendleton, part of
Pendleton-Cold Springs Highway No. 236, became Oregon Route 37. The highway's eastern terminus in Wallula is planned to be moved further north to a new interchange with US 12 after the completion of the
Burbank–
Walla Walla divided highway in the 2020s. ==Major intersections==