[2] In the spring of 1849 Gunnison was assigned as second in command of the Howard Stansbury expedition to explore and survey the valley of the Great Salt Lake.

When he finally returned to Washington, DC, he wrote a book titled The Mormons or Latter-Day Saints, in the Valley of the Great Salt Lake: A History of Their Rise and Progress, Peculiar Doctrines, Present Condition.

After crossing the Tomichi Valley, the survey team encountered the Black Canyon, carved by the Gunnison River which was also named in his honor.

[2][3] The weather was beginning to turn "cold and raw" with snow flurries, and Captain Gunnison sought to speed up mapping before returning to winter quarters.

Several miles upstream of Sevier Lake (about the site of the present Gunnison Bend Reservoir), the team was divided into two detachments.

[7] Most contemporary accounts of the massacre maintain that the Mormons warned Gunnison that his party might be in danger from local bands of Pahvant Utes.

"[8]: 71  But after the killings, rumors circulated that the Pahvants involved in the massacre were acting under the direction of Brigham Young and an alleged secret militia known as the Danites.

However, the Utah Legislature (dominated by LDS officials) had repeatedly petitioned Congress for both a transcontinental railroad and telegraph lines to pass through the region.

[9] When the railroad finally came to Utah, LDS leaders organized cadres of Mormon workers to build the railway, welcoming the income for the economically depressed community.

[11] In 1854 Lieutenant Colonel Edward Steptoe was sent by the War Department to investigate the attack and determine the truth of rumors that Mormons had colluded with the Indians in the ambush.

"[8]: 74 Nevertheless, the Gunnison Massacre resulted in much controversy and added additional strain to the relationship between Governor Brigham Young of the Utah Territory and the federal government.