As settlers moved west, the Shoshone lost their way of life and means to survive.
"They were in starvation mode," said Robert Voyles, director of the Fort Douglas Military Museum.
Brigham Young's policy was to keep peace by giving food to local tribes, but frustrations occasionally escalated. After a miner was killed, a warrant was issued for the arrests of chiefs Bear Hunter, Sanpitch and Sagwitch.
Even though relations with the Northwestern Band of the Shoshone were generally good, Col. Patrick Connor, stationed at Fort Douglas in the Salt Lake Valley, made plans in January 1863 to attack the Indians' winter camp.
"The troops were volunteers who were supposed to go to the Civil War," said Darren Parry, vice chairman of the tribal council. Instead, the soldiers were stuck in Utah, watching the Mormons and guarding mail and telegraph lines. "They were itching for a fight."
The soldiers attacked, and the Shoshone fought back, killing 24. The tide turned about an hour later, when the Shoshones were surrounded and out of bullets.
"The soldiers very quickly had won the day, but they didn't stop there," said Scott Christensen, author of the book "Sagwitch: Shoshone Chieftan, Mormon Elder, 1882-1887" (Utah State University Press, 1999). "They were out to send a message that would never be forgotten."
They went through the camp, killing men, women and children. "There's no effort on the part of Connor and the officers to restrain the soldiers," said Voyles.
Christensen said the killings were witnessed by Mormon settlers from Franklin.
"Those guys wrote letters about what they saw. They were sickened by watching soldiers putting bayonets through the wounded, and raping Indian women as they were in the very act of dying, as one source put it," said Christensen. There were also reports of soldiers killing babies and children by smashing them against hard surfaces.
Connor made no mention of the brutality in his official report. When it was over, the colonel reported finding 224 bodies on the field. Other witnesses put the Shoshone dead at anywhere from 250 to 490.
"There's no way to know the exact number killed," said Christensen, "Some were shot and fell in the river, or hid in the river with injuries and froze and died. ... No matter what numbers you use, this is about as bad as it gets."
What happened along the Bear River was as bad as what happened at Wounded Knee and Sand Creek, say historians -- maybe worse. And yet, nationally, almost no one knows about the Bear River Massacre.
Why do so few remember?
"The most common (reason) that historians give, is that it happened during the Civil War. There were a lot more, bigger and more important, things happening back east," said Rod Miller of Sandy, author of the book "Massacre at Bear River: First, Worst, Forgotten" (Caxton Press, 2008).
The massacre at Sand Creek, Colo., was also during the Civil War, but Miller says it got more attention because of settlers' outrage, which resulted in military and legislative investigations. That didn't happen after the Bear River massacre.
"The Mormons were kind of ambivalent ... some thought the fact that the army killed so many Indians was a blessing, and others really hated the thought, but most didn't talk about it," Miller said.
And they didn't generally communicate their thoughts to outsiders.
"Mormons at that time were very insular," he said. "They didn't care at that time if the outside world even knew Utah existed."