Hartshorne was originally established as a mining town sometime in the 1800's back when Oklahoma was still referred to as "Indian country, or Territory. The coal mines were the main business, employing most of the population of Hartshorne, Adamson, Haileyville, and many of the small communities of the area.
When the demand for coal fell off, many of the mines just closed, leaving many miles, and levels of the mines intact. The tunnel system stretched over the entire county of Pittsburg county, undermining some cities, like Hartshorne, and Haileyville. The only stable example of a mine still around is the Carbon no.3. It is a training school for mine rescues, and is owned by the Bureau of Mines.
I am not sure when the Hartshorne dam was built, but it was built as a water supply for Hartshorne, and i believe it also supplied water for the Rock Island Railroad, as did Dow Lake, about 1-2 miles north of Haileyville, which was on the other side of the Hartshorne city limit line.
The dam is still there , although in desperate need of repair. Some of the water treatment plant is still there but is now posted off-limits by the city.Almost everything else is gone.