From 1853 to 1854, Ives served as a Second lieutenant in the U.S. Army's Topographical Engineers and assisted Lt. Amiel Weeks Whipple in the Pacific Railroad survey along the 35th parallel.

His party included Smithsonian associate John Strong Newberry as geologist and German artist Balduin Möllhausen.

Next day, they went two miles farther to Las Vegas Wash, which Ives thought might be the Virgin River, but had doubts because it seemed too small.

The difficulties encountered in the canon were of a character to prevent a steamboat from attempting to traverse it at low water, and we had seen drift-wood lodged in clefts fifty feet above the river, betokening a condition of things during the summer freshet that would render navigation more hazardous at that season than now.

At the beginning of American Civil War, he declined a promotion to captain and, despite his Northern birth, he joined the Confederate Army in late 1861.