Major General Henry Slocum’s Federal XII Corps arrived on the battlefield during the late afternoon of July 1. Despite its obvious importance, Slocum’s corps did not occupy Culp’s Hill until early the following morning. When he was elevated to command that sector, Brig. Gen. Alpheus Williams of the First Division took charge of the XII Corps. Brigadier General Thomas Ruger moved up to command the First Division, and Col. Silas Colgrove assumed control of the Third Brigade. Brigadier General John Geary commanded the XII Corps’ Second Division.1
Culp’s Hill is actually two hills, with a dip or wide “saddle” yawning between them. Geary’s division occupied the higher of the two hills, with Brig. Gen. George Greene’s brigade anchoring the left and Brig. Gen. Thomas Kane’s brigade deployed on “Pap” Greene’s right. Colonel Charles Candy’s brigade dug in behind its sister units. Colonel Archibald McDougall’s brigade of Ruger’s First Division formed on Kane’s right, with Col. Silas Colgrove’s brigade occupying the Spangler Spring area farther to the right. An independent brigade under Brig. Gen. Henry Lockwood extended the line to the right, facing southeast.
From the top of the upper slope of Culp’s Hill, Greene’s men could look to their left and see Wadsworth’s Federal I Corps division. Kane’s brigade, now under the command of Col. George Cobham, deployed on Greene’s right “at an angle of about 45 degrees forward, conforming its line to the crest of the ridge" in the “saddle” region between the higher and lower hills. Greene deployed his regiments along a 400-yard front from left to right as follows: 78th New York – 60th New York – 102nd New York – 149th New York – 137th New York. Kane’s brigade deployed with the 109th Pennsylvania on the left and the 111th Pennsylvania on its right along the top of the lower hill. The latter regiment’s right flank connected with the 123rd New York of McDougall’s brigade. Kane’s remaining regiment, the 29th Pennsylvania, deployed behind a stone wall about 100 yards to the rear. The 29th’s right flank connected with the left flank of the 3rd Maryland Infantry of McDougall’s brigade.2
The line of McDougall’s brigade ran along the crest of the rocky, wooded lower hill with its right flank extending almost to Rock Creek. There, it connected at an angle with Colgrove’s brigade. McDougall deployed his brigade in two lines of battle. The first line formed near the crest of the lower hill and contained, from left to right, the following regiments: 123rd New York – 20th Connecticut – 46th Pennsylvania. The second line settled behind a stone wall seventy-five yards in the rear, deployed, from left to right as follows: 3rd Maryland – 145th New York – 5th Connecticut.3
Colgrove’s brigade extended the line to the right. A swale or marshy area divided the brigade into two parts. The 107th New York faced Rock Creek on the left at a 45-degree angle to McDougall’s brigade, which it touched just north of Spangler’s Spring. The 13th New Jersey was about 75 paces behind it, massed in double columns. To the southeast, on the other side of the swale in McAllister’s Woods, were the remaining three regiments of Colgrove’s brigade. According to Colgrove, the 2nd Massachusetts formed on the left, facing northeast, the 3rd Wisconsin formed in the center of the line facing east, and the 27th Indiana held the right flank, adjacent to Rock Creek and facing south. Because of this unusual alignment, Colgrove referred to the brigade’s position as forming “three sides of an irregular square.” Rock Creek’s width and depth in this area convinced Colgrove the Confederates would not launch an attack in his sector.
Lockwood’s unassigned brigade, composed of two large but green regiments, formed to the left of the 27th Indiana, extending the line almost to Baltimore Pike. The 1st Maryland Potomac Home Guard was on the right and the 150th New York formed on its left.4