I can find no evidence for that being a motivating reason. The Oregon Territory was enormous, and most of the American West became states very generally no more than three degrees by five degrees in extent.

The petition by settlers north of the Columbia River mentions only distance from the seat of government (Oregon City) and the prospects for future growth and settlement.

The residents of Washington don’t appear to have had strong opinions about either slavery or having free blacks as neighbors, and their response to the call to save the Union was rather tepid. The questions that so fiercely divided the eastern half of the nation seemed quite remote and theoretical to those in the Pacific Northwest. The 1860 Census counted only 30 African Americans living in Washington Territory—all but four of them men.