These guys are from the 2nd Field Artillery (FA) out of  Fort Clayton with a pack 75mm Howitzer which was broken down and carried by the mules. The 2nd FA was an all mule outfit carrying this gun with somewhere between 4 or 6 mules carrying the parts to each gun.  Since this photo was mixed up with the Fort Davis photos, I am presuming that the 2nd FA was on maneuvers in the Fort Davis area.