 By utilizing a railroad tunnel under the Blue Ridge Mountains and then transporting troops to Hanover County on the Virginia Central Railroad, Jackson and his forces made a surprise appearance in front of McClellan at Mechanicsville.Reports had last placed Jackson's forces in the Shenandoah Valley; their presence near Richmond added greatly to the Union commander's overestimation of the strength and numbers of the forces before him.This proved a crucial factor in McClellan's decision to re-establish his base at a point many miles downstream from Richmond on the James River at Harrison's Landing, essentially a retreat that ended the Peninsula Campaign and prolonged the war almost three more years.