During the Civil War, Raynolds participated in the Battle of Cross Keys during the Valley Campaign of 1862 and a year later was in charge of fortifications in the defense of the military arsenal at Harpers Ferry, West Virginia.

[3] William F. Raynolds entered the United States Military Academy at West Point, New York, on July 1, 1839, after being appointed[a] from Ohio.

[5][6] He graduated fifth out of 39 classmates in his class of 1843, which included William B. Franklin, Raynolds's friend Joseph J. Reynolds, and future president Ulysses S.

[8] Raynolds's first assignments from 1843 to 1844 were as an assistant topographical engineer involved in improving navigation on the Ohio River and surveying the northeastern boundary of the U.S. between 1844 and 1847.

[9][10] Over a period of several months, Raynolds and other officers from both the army and navy mapped the best approach route to Pico de Orizaba.

[11] As the expedition left to ascend the mountain, a long pack train of nearly fifty officers, soldiers and native guides departed from the town of Orizaba in early May 1848.

Starting from base camp in the early morning of May 10 nearly two dozen climbers made the final push to the top of the mountain, but only Raynolds and a few others reached the summit.

As no higher peaks were known in North America at that time, Raynolds believed Pico de Orizaba was the tallest mountain on the continent.

[13] After promotion to first lieutenant and then captain, in 1857 he was assigned to design and supervise the construction of lighthouses along the Jersey Shore and the Delmarva Peninsula regions.

Raynolds said the Crow were a "small band compared to their neighbors, but are famous warriors, and, according to common report, seldom fail to hold their own with any of the tribes unless greatly outnumbered.

"[20] Raynolds was impressed with Chief Red Bear and, after assuring him the expedition meant only to pass through their territory and not linger, traded with the Crow for seven horses.

Hutton was the first person of European descent to reach this rock formation in northeastern Wyoming, later known as Devils Tower; Raynolds never elaborated on this event, mentioning it only in passing.

[19] The two parties under Raynolds and Maynadier reunited on October 12, 1859, and wintered at Deer Creek Station, on the Platte River in central Wyoming.

[16][18] Hampered by towering basaltic cliffs and deep snows, Raynolds attempted for over a week to reconnoiter to the top of Togwotee Pass, but was forced south due to the June 30 deadline for reaching Three Forks.

[18][22] Though the Raynolds Expedition was unsuccessful in exploring the region that later became Yellowstone National Park, it was the first federally funded party to enter Jackson Hole and observe the Teton Range.

[16] Research data and botanical specimens, as well as fossils and geological items that had been collected during the expedition, were sent to the Smithsonian Institution but were not studied in detail until after the war.

In 1862, Raynolds was engaged with John C. Frémont's Mountain Department in chasing Stonewall Jackson up the Shenandoah Valley and participated in the Battle of Cross Keys.

[6] Raynolds spent two months recovering from illness after the Valley Campaign, then was assigned as chief engineer of Middle Department and VIII Corps in January 1863.

Promoted to major in the Corps of Engineers, he found himself in charge of the defenses of vital Harpers Ferry, West Virginia, in March 1863 during Robert E. Lee's second Confederate invasion of the north during the Gettysburg Campaign.

[25] As the end of war approached and hostilities with the Sioux Indians loomed, Raynolds's knowledge of and experiences in the Great Lakes region became more important to the army than his command of the fortifications of Harpers Ferry.

[6] Promoted to the permanent rank of colonel on January 2, 1881, Raynolds continued serving with the Corps of Engineers supporting a variety of harbor and river navigational improvements until his retirement in 1884, after a military career spanning forty years.

[30] Raynolds's 1848 expedition to the summit of Pico de Orizaba in Mexico predated what is known as the Golden age of alpinism (1854–65), when many major mountain peaks in the Alps were first climbed.

[12][18][35] The fossil remains of the extinct gastropod Viviparus raynoldsanus was named by Ferdinand V. Hayden in honor of Raynolds after the specimen was collected in the Powder River Basin during the expedition.