At Fort Kearny, Captain Simpson turned over the supervision of his topographical party to his most senior lieutenant, J. L. Kirby Smith, while he traveled in advance as a member of General William S. Harney's staff.

Later on the trail, Simpson sent back instructions for Smith to get a good view of Ash Hollow, noting that such "would make a fine illustration for the report."

"Stopped at Court House Rock on our road today," wrote one of the members of the expedition in his diary on July 25, "and Mills (the photographer) took a picture."

Extant images confirm that the photographers produced negatives of a number of important landmarks along their route—today the earliest surviving views from along the Oregon-California Trail.

By Mills and Jagiello After three and a half long months on the road, the topographical party finally arrived at Camp Floyd, Utah Territory, on September 15, 1858.

Returning to Camp Floyd, Simpson and his crew then drafted a lengthy report describing the roads of Utah Territory, complete with a detailed map.

As the survey team finally settled in at Camp Floyd for the winter, Mills and Jagiello were provided with a room for use as a photographic studio in one of the numerous adobe and wood structures just built at the post.

The following day on Jan. 20, a small delegation of Utes led by the prominent leader and Mormon convert Arapeen, arrived at Camp Floyd to meet the post commander, General Albert S. Johnston.

"The cause lies in some degree in the difficulty, in the field, at short notice, of having the preparations perfect enough to insure good pictures," Simpson wrote in his final report, and "chiefly in the fact that the camera is not adapted to distant scenery."

In May 1859 as he set off on the next leg of his explorations across the Great Basin, Simpson left his photographer behind at Camp Floyd and instead used a sketch artist for the remainder of his expedition.

Meanwhile, he studied law, passed the bar in 1872, and was appointed as a police judge in the district, a position he held for the remainder of his working life.