The parallel ranges of the Blue Ridge, extending from the head-waters of the James to the Susquehanna in mid-course, presented peculiar strategic conditions of which the Confederates were as quick as the government of the United States was slow to take advantage. Rising in the southwest, the twin forks of the Shenandoah, wedged apart by the long and narrow range, or rather ranges, known as the Massanutten, unite near Front Royal, where the valley begins to widen to a plain, and pour their waters into the Potomac at Harper's Ferry. Of the two valleys thus formed, the easternmost, through which runs the South Fork, takes the name of Luray, or, in local usage, Page, from its chief county, while the more western and more important, in the lap of which lies the North Fork, preserves the name of Shenandoah, as well for the river as the county. Through this valley lies the course of the great macadamized highway that before the days of steam formed the chief avenue of communication between Pennsylvania and Virginia. Soon after the valley begins to widen, beyond Strasburg and Front Royal, the Opequon takes its rise in the western range, here known as Little North Mountain, and, flowing northeast, falls into the Potomac below Williamsport. The Cumberland valley continues the valley of Virginia into Pennsylvania, the two being separated by the Potomac, which in this part of its course is usually fordable at many points. Topography was by no means Grant's strong suit, yet he was not long in perceiving that the southwesterly trend of this great valley led and must always lead an invading column at every step farther away, not only from its base on the Potomac, but practically also from its objective at Richmond. Wherefore this zone was useless to the armies of the Union, while for the Confederates it had the triple advantage of a granary, an easy and secure way into Maryland and Pennsylvania, and on the flank toward Washington a mountain wall, cut by numerous gaps, of equal convenience in advance or retreat, besides being a constant menace to Washington as well as to the Union army operating between the Blue Ridge and the Potomac. Thus it was that the Confederate force was able to move speedily and unobserved to the north bank of the Potomac at Williamsport, and there, ninety miles north of Washington, equally distant from Baltimore and from Washington, and actually nearer to the Susquehanna than the capital is, held the whole country at its mercy until the Army of the Potomac could be hurried to the rescue. Grant's first orders to Sheridan were twofold: he was to move south by the valley, no matter where Early might be, or what he might be doing, in full confidence that Early would surely be found in his front; and he was to devastate the valley so far as to destroy its future usefulness as a granary and a storehouse of the Confederate army of Northern Virginia.