1811 On September 16, 1811, the Astorians reached was was known as the Seedskadee River by the local Native Americans. They termed it the "Spanish River," as the Spaniards far to the South called the same waters the Rio Verde. Read more about John Jacob Astor and his fur trading expedition through Wyoming here.
Excerpt from "Astoria" by Washington Irving
The travellers continued their course to the south of west for about forty miles, through a region so elevated that patches of snow lay on the highest summits and on the northern declivities. At length they came to the desired stream, the object of their search, the waters of which flowed to the west. It was, in fact, a branch of the Colorado, which falls into the Gulf of California, and had received from the hunters the name of Spanish River, from information given by the Indians that Spaniards resided upon its lower waters.
The aspect of this river and its vicinity was cheering to the wayworn and hungry travellers. Its banks were green, and there were grassy valleys running from it various directions, into the heart of the rugged mountains, with herds of buffalo quietly grazing. The hunters sallied forth with keen alacrity, and soon returned laden with provisions.
1869 The Cook–Folsom–Peterson Expedition of 1869 was the first formal expedition to explore the Yellowstone region. It was undertaken by David E. Folsom, Charles W. Cook, and William Peterson. On September 16, they crossed the Yellowstone at Tower Fall, then traveled east until they reached the East Fork of the Yellowstone, which today is known as the Lamar River. Read an account of the expedition here.
1888 Have you ever heard of Wisley? An article about the locale appeared in the Cheyenne Daily Sun on September 16, 1888. It was a proposed town to be located on the Cheyenne and Burlington Railroad east of Cheyenne between Arcola and Hereford. In later years, Carpenter was established near this location instead.
1915 Anita King finally reached Cheyenne to present at the Lyric Theater downtown after falling behind schedule due to being lost in the western portion of Wyoming. Read more about Anita King and her "Koast-to-Koast" journey here and here.