Glendo State Park is found in one of Wyoming's most historic areas. Spanish Diggings, suggesting a large area of aboriginal activity, lie just a few miles east of the reservoir. Rising out of the reservoir's east side at Sandy Beach is a series of sand dunes that reach from the Great Divide Basin and the Green River to the sand hills of Nebraska. The Arapaho and Cheyenne Indians arrived in southeastern Wyoming and the North Platte River Basin in the 18th century. The Oglala and Brule Sioux arrived in the 1830s, moving into eastern Wyoming from South Dakota. Tipi rings and a variety of cultural artifacts can still be found at Glendo State Park and the surrounding area. Remember though, removing artifacts is unlawful. Although now mostly covered by water, two or more branches of the Oregon-Utah-California Trail went through the area. Upon close examination you can still see evidence of the historic trail. Fertile ground was an enticement to early farmers and ranchers. At one time some of the finest potatoes in northeastern Wyoming were grown here. Glendo Dam construction began in 1954. The dam was completed in 1957 and the power plant in 1958. The dam is an earth fill structure 2,096 feet long and 167 feet high.