Before there were roads, there were rivers.
The Salmon River was used to transport logs south from the forests where the trees were felled, and a number of sawmills were constructed along its length. Many of these mills were built of limestone, and the mortar used was of poor quality. Today, these mills are falling down and should be explored only with considerable caution. You don't need a stone wall falling on you.
Sawmills required a strong water flow, and were often built just down stream from a waterfall or cascade. Such is the case here at Forest Mills. The top of the falls is dammed, forming a mill pond, and the remains of a penstock system can be found which allowed the mill turbine to be driven by the water pressure created at a point at the bottom of the falls.
There are a couple of old wooden sheds which may have been the original lumber storage sheds, more recently re-purposed as farm buildings.
There is another smaller mill building on the south side of the river, probably a grist mill. It sits on private property. The pool at the bottom of the falls is used as a swimming hole.
This is a very picturesque location. Just be careful near the old walls.