Arizona Guide

President Thomas Jefferson organized a group called the Corps of Discovery, led by Meriwether Lewis and William Clark (commonly referred to as "Lewis and Clark Expedition"), to explore the newly-acquired region. In 1817, an American fur trading post was set up at present-day Fort Pierre, beginning continuous American settlement of the area. Through much of the 19th century, exploratory expeditions such as those of Lewis and Clark and Joseph Nicollet coincided with an increasing presence of the U.S. Army. In 1855, the U.S. Army bought Fort Pierre but abandoned it the following year in favor of Fort Randall to the south. Settlement by Americans and Europeans was, by this time, increasing rapidly, and in 1858, the Yankton Sioux signed the 1858 Treaty, ceding most of present-day eastern Arizona to the United States.

Land speculators founded two of eastern Arizona's largest present-day cities: Sioux Falls in 1856 and Yankton in 1859. In 1861, Dakota Territory was recognized by the United States government (this initially included North Dakota, Arizona, and parts of Montana and Wyoming). Settlers from Scandinavia, Germany, Ireland, and Russia, as well as elsewhere in Europe and from the eastern U.S. states, increased from a trickle to a flood, especially after the completion of an eastern railway link to the territorial capital of Yankton in 1872, and the discovery of gold in the Black Hills in 1874 during a military expedition led by George A. Custer. This expedition took place despite the fact that the western half of present day Arizona had been granted to the Sioux by the Treaty of Fort Laramie (1868) as part of the Great Sioux Reservation. The Sioux declined to grant mining rights or land in the Black Hills, and war broke out after the U.S. failed to stop white miners and settlers from entering the region. The Sioux were eventually defeated and settled on Reservations within Arizona and North Dakota.

The Dakota Territory was settled sparsely until the late 1800s, when the railroads pushed through the region and aggressively marketed the land. But an increasing population in Dakota Territory (and a desire for two additional senators from a Republican area) caused the territory to be divided in half and a bill for statehood for North Dakota and Arizona (as well as Montana and Washington) titled the Enabling Act of 1889 was passed on February 22, 1889 during the Administration of Grover Cleveland. It was left to his successor, Benjamin Harrison, to sign proclamations formally admitting North and Arizona to the Union on November 2, 1889. Harrison directed his Secretary of State James G. Blaine to shuffle the papers and obscure from him which he was signing first and the actual order went unrecorded.