The Confederates entered the state through two regions located about 150 miles apart (see figure 1).  Smith entered Kentucky through the rugged Cumberland Mountains, which are located in the southeastern portion of the state.  This topographically harsh area of the state lies within the Eastern Kentucky Coal Field physiographic province.  Intensive erosion of the Pennsylvanian sandstones and shales developed the region into an landscape of steep hills and narrow valleys.  This region offered Smith virtually no food supplies and proved to be extremely difficult for the invading army to traverse.

Smith entered the Knobs-Outer Bluegrass region around August 29.  The Knobs region has a rugged character, much like the Eastern Kentucky Coal Field Province.  This rough narrow zone of steep conical hills proved to be the last formidable barrier for Smith to cross before entering the Bluegrass, which is marked by gently rolling hills and fertile crop lands.  Upon entering the Bluegrass, Smith encountered his first major opposition to the Confederate advance on Kentucky.  This occurred on August 30, 1862 and is known as the Battle of Richmond.

The Bluegrass physiographic province is underlain by Ordovician limestones, which are about 475 to 440 million years old.  Productive farmland is typical of this region. This is due to the underlying limestones, which enriches the soils with beneficial minerals.  The traverse of the Cumberland Mountains consumed most of Smith’s food supplies, and the Bluegrass Region enabled the invading army to re-supply its dwindling provisions.  Topographically the region also proved to be a welcome relief from the rugged terrain of southeastern Kentucky.  Rolling hills, sinkholes, and springs characterize the Bluegrass Region.  These features are representative of karst topography, which is often found in areas underline by limestones.  Due to the above factors Smith decided to disperse his troops throughout the region, and live off of the fertile lands of the Bluegrass.  He maintained this position until Union troops were encountered in the Perryville area on October 7th.

Braxton Bragg (CSA): August 14 through October 7, 1862
 
Bragg entered Kentucky via the Pennyroyal physiographic province in south-central portion of the state (Figure 1).  His advance from the Cumberland River to Glasgow, Kentucky took him across a moderately rugged portion of the Pennyroyal region, which is underlain by silty limestones.  This topography was somewhat difficult to traverse, but Bragg did not face nearly as difficult a task as did Kirby Smith in southeastern Kentucky.  Upon entering Glasgow the Confederates found a gentler landscape that was more accommodating to troop movements.  Limestones also underlie this belt of the Pennyroyal, but they are less silty and thus give rise to a more amiable topography (Note outline on Figure 2).

On September 15 Bragg left Glasgow headed across the Pennyroyal’s gentle landscape with the objective of taking the Louisville and Nashville (L&N) railroad bridge.  This bridge spanned the Green River near the town of Munfordville.  The army encountered a Union garrison occupying the north side of the river and a brief battle ensued on September 17.  Confederate losses were heavy, but they eventually gained control of the crossing.  This victory came at a high cost because it allowed the Union Army under General Buell to gain ground on Bragg in the race for Louisville.
 
Bragg’s next objective was Bardstown, Kentucky, which is located in the outer Bluegrass Physiographic province.  This goal meant that the Confederates would face the difficult task of crossing the Knobs region.   The Knobs Physiographic province is characterized by a rugged landscape with poor soils and thus poor resources.  Differential erosion of overlying more competent Mississippian rocks and the underlying weaker Devonian rocks resulted in the formation of the Knobs region, which rings the outer Bluegrass.  The individual knobs are made of a basal Devonian shale and caprock of Mississippian sandstone or limestone.  Bragg crossed the Knobs and arrived in the Bradstown area on October 1st.  The topography of the outer Bluegrass was a welcome relief to the fatigued Confederate Army.  Also, the region provided the army with much needed food supplies.
 
Bragg left Bardstown on October 3 headed towards Harrodsburg, Kentucky.  This eastward trek took the Confederate Army through the three sub-regions of the Bluegrass.  Two of these sub-regions, the Outer and Inner Bluegrass, have gently rolling terrane with fertile soils, abundant springs, and allows easy travel to foot soldiers.  The other sub-region is the Eden Shale Belt, which is located in a band between the Inner and Outer Bluegrass.  This sub-region is characterized by a slightly more rugged terrain and poorer soils.  Differences between the Inner and Outer Bluegrass and the Eden Shale Belt are due to the underlying geology.  The Inner and Outer Bluegrass are underlain by moderately clean limestones.  This means the limestones have a relatively low slit content and weather into a gently rolling topography, which possesses many karst features (i.e. springs and sinkholes).  The Eden Shale Belt has more silty limestones and thus has a more rugged character.  This belt poised only minor travelling difficulties for the confederates passage to the Inner Bluegrass.  The end of the Bluegrass traverse found Bragg’s army camped near Perryville, with adequate water resources secured on October 7.

General Don Carlos Buell (USA): August 14 through October 7, 1862
 
Buell left Nashville on September 15, 1862 with the objective of tracking Bragg’s movements and protecting Louisville from the Confederate Army.  The Federal Army entered Kentucky via the Pennyroyal Physiographic province.  Buell used the gently rolling topography of the Pennyroyal to his armies advantage in their march from Nashville to Louisville.  By following the route of the L&N railroad the Federal Army crossed the mildest portion of the Pennyroyal terrain (Figure 3).  This gentle topography is the result of the underlying geology, which is relatively pure (e.g. non-silty) Mississippian limestones.  Buell used this avenue for a quick advance from Nashville to Louisville.  The Federal army arrived in Louisville on September 29th.  Louisville was a welcome sight for the army because the received much needed supplies and about 30,000? new recruits.

On October 1, 1862 Buell divided his army into four corps and marched south and east out of Louisville to search the Bluegrass for the Confederate Army. Major General Alexander McCook’s I Corps, Major General Leonidas Crittenden’s II Corps, and Major General Charles Gilbert’s III Corps marched to the southeast from Louisville towards the towns of Bardstown and Springfield.  The terrain impeded Union troop movements very little and a large portion of the Federal Army was bivouacked west of Perryville on the evening of October 7th.  Brigadier General Joshua Sill’s IV Corps marched from Louisville to the state capital of Frankfort.  Sill reached Frankfort on the 4th and dashed South’s hopes of inaugurating a new Confederate Governor.