"Plymouth Rock to Puget Sound" was the motto of the Yellowstone Trail, America's first transcontinental highway, established in 1912.
Interstate 90 was not the first road in the United States to connect east to west. In fact, I-90's route through the Silver Valley closely follows that of its earliest predecessor, the Yellowstone Trail. The Trail was inspired by J.W. Parmley of Ipswich South Dakota in 1912. Parmley and his business partners needed a good road from Ipswich to Aberdeen, twenty-five miles away. Their intent rapidly expanded. Soon their road would extend to the next town, then to North Dakota, then on to Yellowstone National Park. Eventually, Parmley envisioned "a good road from Plymouth Rock to Puget Sound."
The Yellowstone Trail Association was established in 1912 with its headquarters located in Minneapolis. This organization did not actually build roads. Instead it helped local chapters raise money and provided instructions for road construction and maintenance. The Yellowstone Trail Association also worked to promote domestic tourism, printed maps and pamphlets which they handed out along the trail, and advocated the automobile for long distance trips.
The Yellowstone Trail Association was a particularly successful example of the Good Roads Movement, In the late 19th century bicyclists and then automobile owners organized politically to push for improved roads. By 1920 The United States had over 200 named auto trails, though only two, the Yellowstone and Lincoln highways, were trans continental in scope.
The Yellowstone Trail cut through Idaho as the Interstate does today. After leaving Montana, the trail passed through the towns of Mullan, Wallace, Kellogg, and Cataldo. From here, the trail descended into Fourth of July Canyon, while the interstate today climbs the pass. The trail then passed through Coeur d'Alene and Post Falls before crossing into Washington. Few people remember the Yellowstone Trail as being the first northern transcontinental highway. However, to the communities it passed through, it meant tremendous social and economic opportunity.