Pat,

As a starting point, go to the National Park Service's web site for Civil War Soldiers and Sailors

www.itd.nps.gov/cwss/soldiers

Also go to Ken Jones super web site for a little more info on the 31st Cavalry and lots more info on Texas CSA units and other links
www.tarleton.edu/~kjones/CStx

Try those for starters.
By the way, I found a C.O.Evans in the 31st Texas Cavalry.
Good Hunting , Craig