Here’s the units I found from a Goggle Search of the Confederate Order of Battle, Arkansas Post.

First Brigade
Col Robert R. Garland

6th Texas: Ltc T. S. Anderson
24th Texas Cavalry (dismounted): Col C. C. Gillespie
Arkansas Battery: Cpt William Hart
Louisiana Cavalry: Cpt W. B. Denson
Second Brigade
Col James Deshler

10th Texas: Col Roger Q. Mills
15th Texas Cavalry (dismounted): Maj V. P. Sanders
17th Texas Cavalry (dismounted):[1] Col James R. Taylor
18th Texas Cavalry (dismounted): Ltc John T. Colt
Third Brigade
Col John W. Dunnington

19th Arkansas: Ltc A. S. Hutchinson
Note: Unit organization in Third Brigade is incomplete. The following units are known to have been in Fort Hindman during the battle, but served unattached:

24th Arkansas (detachment): Col E. E. Portlock, Jr.
Louisiana Cavalry: Cpt L. M. Nutt
Texas Cavalry: Cpt Alfred Johnson
Texas Cavalry: Cpt Samuel J. Richardson

......

Here is the closest G. Riley I could locate, no J. Riley in the roster:

George J. Riley, age 23, Private, Company A, 6th Texas Infantry, enlisted May 11, 1862 in Lavaca County by Lt. Breeden for the war, reported sick in General Hospital at White Sulphur Springs , Arkansas September 11, 1862, died September 27

The 6th (also called 3rd) Regiment Texas Infantry was formed of ten companies which were mustered into the Confederate States service from September 27, 1861, to April 11, 1862. Most of the regiment surrendered at Arkansas Post, January 11, 1863, and was exchanged east of the Mississippi River, where it was consolidated with similar remnants of the 10th Regiment Texas Infantry and the 15th Regiment Texas Cavalry about May, 1863.

M323: Compiled Service Records of Confederate Soldiers Who Served in Organizations from the State of Texas