Henry S. Tanner and Cartographic Expression of American Expansionism
The above trio of links explores American interest in the Pacific Northwest before genuinely interest ramped up in the 1840s. Apparently it was the official American position to try to make the 49th parallel extend to the Pacific Ocean in the 1818 Convention negotiations, and a number of Congressmen in 1820-1824 - John Floyd (VA), Francis Baylies (MA), and Thomas Benton (MO) - advocated a very early settlement of the Columbia River valley, with an "Origon Territory" being incorporated into the Union come two thousand peoples' worth of settlement. In response to the sheer distance and Rocky Mountains barriers, they noted 1) Kentucky was seen as distant and unable to be integrated in 1775, 2) steamships were already making the rivers very easy to travel (and it must be noted the Missouri River to Fort Benton and Columbia-Snake to Lewiston ID is navigable just fine by them), 3) Americans had already crossed the Appalachian Mountains and settled past the Mississippi River within the lifetime of those who won independence to the then-current 1820s, 4) the Pacific Ocean was as good a border as any, and 5) the Pacific-Asian trade and local forestry/farmland would help pay for things, of course. Those who opposed it, meanwhile, 1) kept stressing the sheer distance and Rocky Mountains, as well as the local area perhaps not being suitable enough for settlement via its thick forests, 2) if it was settled the distance would cause the locals to develop a mind of independence, 3) and that Britain already had a sincere toehold via the Hudson Bay Company's local fur-trapping activity. Absolutely vital to note is that this all was discussed and advocated before the first American railroads were built in the latter half of the 1820s.
BUT: assume the 49th parallel to the Pacific is set as the border in 1818, the first proposal to settle Oregon in 1820 does indeed lead to settlement of the Pacific Northwest shortly after, and an earlier Oregon Trail and Oregon Territory definitely established if still admittedly newly-so by the end of the decade at 1830 . Again, before railroads became common and caused distance to become a non-issue. Could the Pacific Northwest become a fully-established, integral/-grated part of the Union pre-railroads or would the distance and Rocky Mountains prevent it from effectively being so?