J.O.,

A company of the 1st Texas Cavalry ( aka 1st Texas Mounted Vols, 1st Texas Mounted Rifles , Buchel's Regiment, etc. ) was engaged with "the enemy" near Eagle Pass , Texas in 1864. This was only one of countless encounters that CSA and Texas State Troops, Militia and Texas Rangers had along the border with "the enemy". The "enemy" could include Union troops operating out of Brownsville and other locations such as Laredo , after it was recaptured ; it could include Indians ( anyplace , anytime ) it could include Mexican troops ( regular and irregular troops who were also fighting the French who were trying to take over Mexico and were somewhat sympathetic to the CSA) and it could have included bandit groups , which would have been made up of some of all of the above groups plus deserters from all sides, except the Comanches ; you didn't desert from the Comanches. In all seriousness, the Texas - Mexico border has always been a dangerous place ( as it continues to be today , for some different reasons than in WBTS period) . I've hunted white tail deer along the border areas in south Texas and west Texas for 20 years and I speak from personal experiences .

The Texas Rangers , Texas State Militia and a handful of CSA Cavalry units , did yeoman service along the border during the war to do the best they could do to protect the populace from " the enemy". Let me quickly add that Col Santos Benavides and his ( largely Hispanic ) CSA mounted troops provided an outstanding service to the border area for the Texians who were trying to scratch out a living in a hostile ( still is , in my opinion) environment. Thanks to the excellent writings of Dr Jerry Thompson and a few others , Col Benavides and his men have received credit for the service they provided . See Dr Jerry Thompson's book ,"Vaqueros in Blue and Gray" .
There are two additional books ( both in softcover), that may shed some more light on possible actions that your ancestor may have been involved in; "Texas , Dark Corner of the Confederacy" and Texas Frontier Defense during the Civil War. I think I have the last title messed up but some board reviewers will no doubt , clean up my attempt to name the book .
Good Hunting , CAM