The U.S. Army established Platte Bridge Station in 1862 to protect the Oregon/California/Mormon Trail crossing of the North Platte River and the new transcontinental telegraph. After Lt. Caspar Collins was killed there by Cheyenne and Lakota Indians in 1865, the post was renamed Fort Casper, misspelling his first name. The fort was abandoned two years later, but reconstructed in 1936—and renamed Fort Caspar—with funds from the Works Progress Administration. Fort grounds and a museum are open to the public.

The Connor Battlefield is a park on Tongue River in Ranchester, Wyo., marking the spot where Brig. Gen. Patrick Connor and about 475 U.S. troops and Pawnee scouts in August 1865 attacked a village of 500 Arapaho under the leadership of Black Bear and Old David. The Arapaho suffered 33 killed, and the troops burned their lodges and drove off most of the horse herd. Today the park offers picnic grounds, a campground and a monument to the event.