Below Canada, the geologic nature of successive barrier ridges of the Ridge and Valley Appalachians run from the valley of the Hudson, the Delaware Water Gap, down through all of northern Pennsylvania, sundering eastern and central Pennsylvania, Maryland, and North Carolina, Virginia from the eastern Great Lakes, Western Pennsylvania, West Virginia, West Kentucky, and Western Tennessee. Different gaps of the Allegheny had slopes that were more or less amenable to foot travel, pack mules, and possibly wagons, allowing Native Americans and the occasional trader, using one of the Kittanning Paths, and then, after about 1778-1780, settlers, to travel west into the relatively depopulated Ohio Country; the gaps, like the other two major breaks inside the Appalachians barrier mountain chain, the Cumberland Narrows and Cumberland Gap well to the south, were the only ways to cross into the central lowlands of the Mississippi valley in the long decades before the railroads were born and tied the country together with steel using each as a transportation corridor ever since. Right up until the engineering projects that began with the political movement to connect cities and towns with roads better than dirt tracks in the 1920s, there simply were no ways in most areas to transit the barrier of these mountains without well developed wilderness skills.