"I turned around and counted them back and counted just the same," Jasperson writes. He was just 19 at the time of the massacre.
That is a far higher number than previous accounts of the Jan. 29, 1863, massacre when the U.S. Army's Third California Volunteers - intent on punishing the region's Indians for pestering mining supply wagons and pioneers in Cache Valley and along the California Trail - rode from Fort Douglas in Salt Lake City, surrounded the Shoshones on the banks of the Bear River near Preston, Idaho, and slaughtered most of four bands.
Accounts at the time said 210 to 300 Shoshones were killed (17 soldiers died on the battlefield and several more died of their wounds later).
The highest previous number - nearly 400 Shoshones - was reported by three pioneers who rode horses through the battlefield the next day, says historian Scott Christensen, who wrote a biography of Sagwitch, a surviving chief.
Even at the lower estimates, the Bear River Massacre stands as the worst in the western United States since the nation was founded.
Christensen and another historian described Jasperson's autobiography as "exciting" new information, although it will require much more research.
"Assuming it's true and accurate, it is very, very significant," said Bob McPherson, who teaches history at College of Eastern Utah's San Juan campus in Blanding. He specializes in military and American Indian history, and has led military group tours of the Bear River battleground.
Family documentsMerrill Nelson is a retired accountant living in West Valley City who, realizing it could be significant, last year sent his great-grandfather's autobiography to the Northwestern Band of the Shoshone Nation.
But he doesn't know how to check out the veracity of the account. He knows of no original journal, although one is mentioned in a separate biography written by his great-aunt.
"We don't really have any idea about it," he says.
All Nelson has are two documents, a typed copy of Jasperson's 1911 autobiography -- written in the first person, but labeled a biography and witnessed by a grandson -- and a 1913 handwritten and signed letter in which Jasperson seeks compensation from the Utah Legislature for fighting Indians during the Indian Wars.
Both were left behind by his mother, a family-history buff, who received them from her mother, Jasperson's oldest daughter.
In both, Jasperson writes that he saw 493 bodies.
The 11-page autobiography touches on the massacre in just two matter-of-fact paragraphs. The rest details other exploits, like helping pioneers make the long trek to Utah, marrying and raising a family on a farm in Goshen near Payson.
Jasperson, young but already experienced driving oxen teams, writes that he was hired to go to the Salmon River country (mining camps) and, as he was headed through northern Utah, came across Mormon frontiersman Lot Smith, who told him the Army was fighting the Indians up the river.
Jasperson writes that he went with "him," implying Smith, to the battleground.
His description of the battlefield - indeed most of the autobiography - rings true, said Christensen. The verbiage fits the era, and Jasperson does not seem to exaggerate. The topographical details he supplies are accurate.
Two aspects, however, trouble Christensen.
Jasperson writes that Lot Smith told him the Indians had killed 60 soldiers and wounded 60 more, numbers far higher than the military casualties at Bear River.
"It's fairly compelling as history, but I can't square that," Christensen says,
Jasperson also does not mention Shoshone bodies piled eight and five deep, as the three pioneers who rode through the battlefield described, Christensen notes.
Christensen says he has not researched whether Lot Smith was at the Bear River, but it's possible.
Smith was a good friend of Porter Rockwell, according to a short biography in the University of Utah Marriott Library's Special Collections, and it was Rockwell who led the soldiers to the Shoshones' winter camp along the Bear River.
'Better understanding'Christensen, a historian for The Church of Jesus Christ of Latter-day Saints, says he hopes the Jasperson autobiography will spur more research and analyis.
"Hopefully we can keep piecing it together and get a better understanding," he says.
Patty Timbimboo Madsen, the Northwestern Band's natural-resources manager, says the few Shoshone survivors of the massacre did not speak much about how many men, women and children died.
Her aunt, Mae T. Parry, however, listened to the stories of survivors and argued in her essay, "Massacre at Boa Ogoi," that the military engaged in wholesale slaughter of her people.
The tribe's written history estimates 350 died that day.
If the casualties were in fact higher, says Madsen, it will affirm Parry's conclusion.
"The only thing it does is tell me that the stories my Aunt Mae told were true stories, that it wasn't a battle. It was a massacre."
Parry died last spring.