View of the moment witnessed by Capt. James H. Carleton "when O'Brien was so gallantly striving to hold the Mexicans in check during their last attack upon the great plateau."  It occurred while the Kentucky and Illinois infantry were meeting with disaster in the ravine (depicted by the thin strip of smoke, middle right).  A large mass of attacking Mexican infantry (center, in distance) threatens Gen. Taylor and his staff (foreground).   Nothing stands between them but a battery of three guns under Capt. John P. O'Brien (center). Another gun, commanded by Capt. Braxton Bragg, has just arrived in the right foreground.  At far left is Col. Jefferson Davis' 1st Mississippi Infantry and Gen. Joseph Lane with the 3rd Indiana and remnants of the 2nd Indiana rushing to the weak point.

O'Brien saw that if he stood his ground and fought until his guns were captured there was a chance remaining to retrieve the fortunes of the day.  By the time he was captured, nearly all of his battery had been killed or wounded.  But, they hung on long enough: Bragg, Davis and Lane and their troops arrived to repel the last Mexican assault.  During the night the Mexican army retreated down the valley to the south.  Taylor reported 272 killed and 387 wounded. The Mexican losses were estimated at double that number.  The battle left the Americans in control of Northern Mexico.