Bill, off the top of my head I can't say who immediately succeeded in command on the field, but the senior captain was Capt. William T. Hicks, Co. A. His date of rank was February 22, 1862, back when the outfit was a two-company cavalry squadron commanded by Capt. Richard Hooker.

Immediately after the battle at Prairie Grove, the following promotions were made in camp at Van Buren:

Maj. Lucien C. Gause, to colonel, December 9, 1862.
Capt. William T. Hicks, to lieutenant-colonel, December 10, 1862.
Capt. Arthur F. Stephenson, to major, December 9, 1862.

As you know, just before Prairie Grove, Col. Charles H. Matlock had resigned on a surgeon's certificate of disability on November 7, 1862.