A few days ago I stopped by to study the historical makers about Valley Mill in order to get some idea of its location and to try to determine if the nearby brick house is the same one referenced on one of the markers. While I was there, a young man came out of the house. He turned out to be a friendly guy who was a park policeman who rented the house from the county. He verified that it was the same house mentioned on the historical marker and that it was built in 1793.
I brought up that the marker also said that the foundation for the mill still existed and asked him if he knew where I could find these remains. He said he didn't know, but I thanked him before he went on to work.
His information was helpful to me because he verified the house was the same one as the one in the photo taken in the 1930's which was reproduced on one of markers. Since the house and the mill appeared to be close by in the photo, I snooped around the property after he left. I found stacked stones mostly hidden by vegetation, and I think it's likely the stones were what's left of the foundation although I suppose they could have been part of a stone fence.
Soon after I retired, Pam and I took a course on the archeology of Montgomery County. I remember from the course that the database of designated archeological sites in Maryland was difficult to get authorization to access because the state didn't want people disturbing the sites and removing artifacts. That's okay because doing the detective work yourself can be satisfying.