The biggest problem Arizona's military faced was that they had too few soldiers for too vast of a land. Although most chronicles of the time regarded Apaches as the biggest menace, but Yuman-speaking Yavapais, who were usually identified as Apache Mohaves or Apache Yumas, resisted Anglo intruders just as tenaciously. Divided into four subtribes, the Tolkapaya (Western Yavapais), the Yavepe and the Wipukpaya (Northeastern Yavapais), and the Kewevkapaya (Southeastern Yavapais), the Yavapais ranged from the Colorado River to the Tonto Basin. Like the Apaches, they were mobile and extremely independent, their only political authorities being war chiefs and advisory chiefs selected by local groups. This made it extremely difficult for the U.S. military to run down or negotiate with more than one Yavapais group at a time. Troopers, many of them German and Irish immigrants, had to persue the Yavapais across rough desert terrain. Many of the soldiers deserted, fleeing places like Camp Grant, a sun-scorched collection of adobes.
Early in 1871 a 37 year old first lieutenant named Royal Emerson Whitman assumed command of Camp Grant on the San Pedro River about 50 miles (80 km) northeast of Tucson. In February 1871 five old Apache women straggled into Camp Grant to look for a son who had been taken prisoner. Whitman fed them and treated them kindly, so other Apaches from Aravaipa and Pinal bands soon came to the post to receive rations of beef and flour. That spring, Whitman created a refuge along Aravaipa Creek about five miles (8 km) east of Camp Grant for nearly 500 Aravaipa and Pinal Apaches, including Chief Eskiminzin. The Apaches began cutting hay for the post's horse and harvesting barley in nearby ranchers' fields.
Whitman may have suspected that peace could not last. He urged Eskiminzin to move his people to the White Mouintains near Camp (later Fort) Apache, which was established in 1870, but he refused. During the winter and spring, William Oury and Jesús María Elías formed the Committee of Public Safety, which blamed every depredation in southern Arizona on the Camp Grant Apaches. After Apaches ran off livestock from San Xavier on April 10, Elías contacted his old ally Francisco Galerita, leader of the Tohono O'odham at San Xavier. Oury collected arms and ammunition from his fellow Anglos.
On the afternoon of April 28, six Anglos, 48 Mexicans, and 94 O'odham gathered along Rillito Creek and set off on a march to Aravaipa Canyon. At dawn on Sunday, April 30, they surrounded the Apache camp. O'odham were the main fighters, while Anglos and Mexicans picked off any Apaches that tried to escape. Most of the Apache men were off hunting in the mountains. All but eight of the corpses were women and children. Twenty-seven children had been captured and more than 100 Aravaipas and Pinals had been mutilated and slain.
Lieutenant Whitman searched for the wounded, found none, buried the bodies, and dispatched interpreters into the mountains to find the Apache men and assure them that his soldiers had not participated in the "vile transaction." The following evening, the surviving Aravaipas began trickling back to Camp Grant. Most of the settlers in southern Arizona considered the attack justifiable homicide and agreed with Oury. The U.S. military and Eastern press called it a massacre. President Grant informed Governor A.P.K. Safford that if the perpetrators were not brought to trial, he would place Arizona under martial law. The trial lasted five days, and after 19 minutes of deliberation, the jury acquitted every defendant.
Many army officers considered the trial a travesty and believed that a nefarious "Tucson Ring" of freighters and government contractors had encouraged the Camp Grant Massacre in order to provoke the Aravaipas and keep supplies flowing to the troops, though the arguments made the common mistake in Western history of attributing the massacre to Anglos when the leading participants had been O'odham or Mexicans.