Morgan's Arkansas regiment was in the same brigade as Pleasants' regiment. Here are references to where Morgan's regiment was leading up to August 28, 1862:

Asa S. Morgan Civil War letters
Butler Center for Arkansas Studies

8/13 Camp Crystal Hill-A.S. Morgan to My Dear Wife-The first Bgde of this Division, Col Sweet cmdg, consisting of five Texas Regts move d at 2 oc this morning for Bayou Metre in the direction of Brownsville. It consists of Sweet’s, Taylor’s, Fitzhugh’s, Daniel’s and Nelson’s Regts. The second Bgde, Col McRae cmdg, consisting of Pleasants’, McRae’s, Johnson’s Matlock’s, McNeil’s & Morgan’s six regs will move at 5 P.M. this eve for said place, all under command of Col Nelson...
My own, Col. Pleasants & Col. Nelson’s Regs that made the other campaign on the White River are _____ by sickness. I have over 350 sick in camp. The three Regs are about 3000 strong and cannot _____ out 600 men. I and Pleasants report for duty each about 170 men.

8/18 Camp Crystal Hill-A.S. Morgan to My Dear Wife-...I am ordered to start at 2’oc to day now 1.30” to Austin in Prairie County 30 miles from Little Rock and 15 from Brownsville to select a camping place for our Division.
The 1st Bgde, Col Sweet (Texas) leaves in the morning, the 2d Col McRae (Arkansans) next morning – in all 11 Regts – we have been almost without water since we came to this camp except river which is unfit to drink and dozens of our men have died.
I have lost 1 to 2 every day and now have 370 sick in camp to say nothing of those on furlough and in hospitals. We protested until it was no use, but God be praised, Genl. Holmes does not see things as those who preceded him and we move away from this river to good water. It was worse than cruel to keep us here when water could be procured by going a few miles to it.
We all blame a Col Shoup, Genl. Hindman’s adj genl who is responsible for this camp. Gen. Hindman never saw it but when we came would not let us leave...

8/20 [Morgan's Ark regt] left Crystal Hill & marched to Camp Hope, Austin-30 miles

8/23 Camp Hope Near Austin-A.S. Morgan to My Dear Wife-... We are now encamped on one of the most pleasant neighborhoods I have ever seen in the State, with an abundance of the finest spring water and plenty of fruit and already the improvement is manifest in the health and spirits of the men.
If we can remain at this place a few weeks I think we would all get on our feet and had we been here during our stay at Crystal Hill it would have made an immense difference in the condition of these men.
Genl. Hindman committed an egregious error (sin) in putting us there and then persisting in keeping us there in the now _____ who here expect o soon be well, would have been buried there – as a small spring our only chance for drinking water. There was a line from 50 to 200 waiting to get a drink, and then would be there in like number drinking the whole night

SAN ANTONIO HERALD, Sept 27, 1862
9/2 Camp Hope, 1st Brig. 1st Division, Army of SW-to newspaper from Tx Bgde AG Henry Logan. . . There are two Bgdes here, about 25 miles from Little Rock, on the Searcy road...
The Ark Bgde consists of six regiments, and is commanded by Col McRae...