On July 1, 1898, at about 10am, the Rough Riders and the 10th Cavalry were stationed below Kettle Hill.
The Spaniards, who were on top of the hill, [Mauser] rifle fire down on the Americans.
Buckey O'Neill was killed in action.

Theodore Roosevelt, commander of the Rough Riders, wrote about the death of O'Neill: 
The most serious loss that I and the regiment could have suffered befell just before we charged.
O'Neill was strolling up and down in front of his men, smoking his cigarette, for he was inveterately addicted to the habit.
He had a theory that an officer ought never to take cover—a theory which was, of course, wrong, though in a volunteer organization the officers should certainly expose themselves very fully, simply for the effect on the men; our regimental toast on the transport running, 'The officers; may the war last until each is killed, wounded, or promoted.'
As O'Neill moved to and fro, his men begged him to lie down, and one of the sergeants said, 'Captain, a bullet is sure to hit you.'
O'Neill took his cigarette out of his mouth, and blowing out a cloud of smoke laughed and said, 'Sergeant, the Spanish bullet isn't made that will kill me.'
A little later he discussed for a moment with one of the regular officers the direction from which the Spanish fire was coming.
 As he turned on his heel a bullet struck him in the mouth and came out at the back of his head; so that even before he fell his wild and gallant soul had gone out into the darkness.

Before the fighting was over, O'Neill's men had buried him on the slope of San Juan Hill.
After the war, his family and friends enlisted help from the War Department to find and recover his body.
After six men failed to find the site, the War Department sent Henry Alfred Brown, the Rough Riders' Chaplain, to find him.
Despite it being eight months since O'Neill's death, Chaplain Brown located the site within two hours after arriving in Santiago.
 The well preserved body was exhumed, placed in a coffin, and returned to the United States on the Army transport Crook.
He was reinterred in Arlington National Cemetery, Section 1, Site 294.
The epitaph on his gravestone reads,"Who would not die for a new star on the flag?"

On July 3, 1907, a monument by sculptor Solon Borglum was dedicated to O'Neill and the other Rough Riders in their memory in Prescott, Arizona.
Seven thousand people gathered to witness the unveiling.

O'Neill Spring, in the Pumphouse Wash wetlands south of Flagstaff, was named after Buckey O'Neill.
On July 1, 1898, at about 10am, the Rough Riders and the 10th Cavalry were stationed below Kettle Hill. The Spaniards, who were on top of the hill, [Mauser] rifle fire down on the Americans. Buckey O'Neill was killed in action.
Theodore Roosevelt, commander of the Rough Riders, wrote about the death of O'Neill: 
The most serious loss that I and the regiment could have suffered befell just before we charged. O'Neill was strolling up and down in front of his men, smoking his cigarette, for he was inveterately addicted to the habit. He had a theory that an officer ought never to take cover—a theory which was, of course, wrong, though in a volunteer organization the officers should certainly expose themselves very fully, simply for the effect on the men; our regimental toast on the transport running, 'The officers; may the war last until each is killed, wounded, or promoted.' As O'Neill moved to and fro, his men begged him to lie down, and one of the sergeants said, 'Captain, a bullet is sure to hit you.' O'Neill took his cigarette out of his mouth, and blowing out a cloud of smoke laughed and said, 'Sergeant, the Spanish bullet isn't made that will kill me.' A little later he discussed for a moment with one of the regular officers the direction from which the Spanish fire was coming.  As he turned on his heel a bullet struck him in the mouth and came out at the back of his head; so that even before he fell his wild and gallant soul had gone out into the darkness.
Before the fighting was over, O'Neill's men had buried him on the slope of San Juan Hill. After the war, his family and friends enlisted help from the War Department to find and recover his body. After six men failed to find the site, the War Department sent Henry Alfred Brown, the Rough Riders' Chaplain, to find him. Despite it being eight months since O'Neill's death, Chaplain Brown located the site within two hours after arriving in Santiago.  The well preserved body was exhumed, placed in a coffin, and returned to the United States on the Army transport Crook. He was reinterred in Arlington National Cemetery, Section 1, Site 294. The epitaph on his gravestone reads,"Who would not die for a new star on the flag?"
On July 3, 1907, a monument by sculptor Solon Borglum was dedicated to O'Neill and the other Rough Riders in their memory in Prescott, Arizona. Seven thousand people gathered to witness the unveiling.
O'Neill Spring, in the Pumphouse Wash wetlands south of Flagstaff, was named after Buckey O'Neill.
Buckey O'Neill