On the southern end of the battlefield, Union soldiers commanded by Col. Franz Sigel launched a surprise attack on Confederate camps as part of a plan in which Sigel attacked from the south while General Lyon attacked from the north. On the morning of the battle, Sigel's men occupied a ridge across the creek, and when Gen. Lyon's cannon opened fire to the north, Sigel began shelling the 2,300 Confederate cavalrymen camped in Sharp's Cornfield. The exploding shells drove the startled Confederates northward, and by 7:30 A.M. Sigel had crossed the creek and entered the far end of the field. Col. Elkanah Greer's Texas Cavalry Regiment then stood in line of battle to stop the Union advance, but Sigel's artillery fire forced the Texans back, allowing him to move into a position blocking the Wire Road. In his official report to Major General John C. Fremont, Sigel wrote that his brigade had been ordered to attack the enemy in the rear and cut off his retreat, and he said that artillery placed on a little hill fired on the enemy camp with such effect that the troops left their tents and hurried toward the northeast of the valley. He also reported that when the enemy rallied in large numbers, about 3,000 infantry and cavalry, he brought the artillery forward, formed a battery across the valley with the Third and Fifth Regiments to the left and the cavalry to the right, and after an effective fire of half an hour the enemy retired in some confusion into the woods and up the adjoining hills.