By April 1864, Maj. Gen. Nathaniel P. Banks’s Red River Expedition had advanced about 150 miles up Red River. Maj. Gen. Richard Taylor, commander of the Confederate forces in the area, decided, without any instructions from his commander Gen. E. Kirby Smith, that it was time to try and stem this Union drive. Taylor gained a victory at Mansfield on April 8. Banks withdrew from that battlefield to Pleasant Hill, but he knew that fighting would resume the next day. Early on the 9th, Taylor’s reinforced forces marched toward Pleasant Hill in the hopes of finishing the destruction of the Union force. Although outnumbered, Taylor felt that the Union army would be timid after Mansfield and that an audacious, well-coordinated attack would be successful. The Confederates closed up, rested for a few hours, and then attacked at 5:00 pm. Taylor planned to send a force to assail the Union front while he rolled up the left flank and moved his cavalry around the right flank to cut the escape route. The attack on the Union left flank, under the command of Brig. Gen. Thomas J. Churchill, succeeded in sending those enemy troops fleeing for safety. Churchill ordered his men ahead, intending to attack the Union center from the rear. Union troops, however, discerned the danger and hit Churchill’s right flank, forcing a retreat. Pleasant Hill was the last major battle, in terms of numbers of men involved, of the Louisiana phase of the Red River Campaign. Although Banks won this battle, he retreated, wishing to get his army out of west Louisiana before any greater calamity occurred. The battles of Mansfield and Pleasant Hill jointly (although the former was much more decisive) influenced Banks to forget his objective of capturing Shreveport.

From a marker near Clear Lake, IA regarding the battle:

The Battle of Pleasant Hill can be considered as day two of the Battle of Mansfield, or Sabine Cross Roads. Due to the single, narrow road available for advance the Union Army, consisting of infantry, cavalry and supply and medical wagons, was strung out over many miles. A.J. Smith's Division of the 16th Corps, of which the 32nd Iowa Infantry Regiment was part of the Second Brigade under Col. W.T. Shaw, was assigned the last position in the column behind the rest of the army.
The head of the column ran into Confederate resistance south of Mansfield at Sabine Cross Roads on April 8th. About 4 p.m., after a couple hours of positioning and skirmishing, a Confederate assault was launched. The Federal line, outnumbered two-to-one due to the strung out nature of the column and order of march, soon collapsed into retreat. That retreat was turned into a near-rout when the retreating men collided with their own supply train. Finally, a rearguard action halted the Confederate pursuit. When darkness fell, Banks ordered the defeated army to regroup at Pleasant Hill.
On the night of April 8th, the 32nd Iowa went into camp near the town of Pleasant Hill, expecting to continue the march the following morning. They were about 20 miles behind the head of the column and only vaguely aware of the fight far from the front. During the night, thousands of terror-stricken men fleeing the disaster near Mansfield stampeded through the encampment. The division was put under arms just after midnight.
At 10 a.m., the four regiments of Shaw's Brigade (including the 32nd Iowa) was ordered to the extreme front and placed at a right angle to the Mansfield Road about 1½ miles west of Pleasant Hill. The 32nd held the extreme left of the brigade. Two other Iowa regiments (the 27th and 14th) lined up beside it near the road and the 24th Missouri Infantry Regiment lined up north of the road. While the brigade held the center of the line, significant gaps on both sides left the unit somewhat isolated and greatly so after the battle began and supporting units on both sides of the brigade fell back.
The Confederate attack began about 5 p.m., concentrating against the center and Union left. The Federal forces on the left were flanked and they were forced to retreat. Soon the battle was in full force well behind Shaw's Brigade. The two Iowa regiments and the Missouri regiment were pulled back, but the order never reached Col. Scott, leaving the 32nd Iowa alone, soon surrounded, and fighting in three directions at once. For another two hours, the battle raged before rallying Union forces drove the Confederates back to their original line and the 32nd Iowa was among friendly forces again.
The 32nd entered the battle with 469 men able to carry a weapon. Col. Scott reported that he lost 210 men killed, wounded or missing in the battle.
The evening, after the battle, General Banks held a war council and decided that retreat was the only option for the Federal forces. Interestingly, Confederate forces believed that they had been defeated by the Federals and they too began their retreat at daylight. Due to loss of wagons, medical supplies and previous orders to clear the roads in case a retreat was needed, all of the Union wounded were left behind and tended to by the residents of Pleasant Hill and some Union physicians who allowed themselves to be taken as prisoners of war by the Confederate forces. Those of the 32nd Iowa who died on the field of battle or of their wounds were buried in Mansfield, Pleasant Hill or near where they received care. Some of those individuals were later disinterred and reburied at the National Cemetery in Alexandria, Louisiana, many in unmarked graves. Other burial locations were never found and the final resting places remain unknown.
Total Forces
Union 25,000 · Confederate 11,000
Casualties
Union 3,980 · Confederate 3,976
Bibliography
Stuart, Addison A. Iowa Colonels and Regiments: Being a History of Iowa Regiments in the War of the Rebellion. Des Moines, Iowa: Mills and Company, 1865.