According to the Ski Club of Washington DC website, from 1948 to ???? there was a portable rope tow used in Rock Creek Park. I would guess that lasted no later than 1951, when they developed Cabin Mountain.
Before that, they went to ski in Glencoe, PA, but no lift service.

Pittsburgh Ski club maintained a small tow and slope at their club cabin at Pine Slopes from 1964 to 1988(?). Pine Slopes road appears to be west of the 381/711 intersection near Seven Springs.

Some time in the 80s, I recall there being a small ski area North of Blue Knob, somewhere in site of US 22 near holidaysburg, PA. Does anyone else recall this? Would have been right along the Pittsburgh/State College travel route before the big I 99 realignment.

More new lost ski area site suggestions as I come up with them.

In the late 70s and early 80s there was a small ski area located between Duncansville and Altoona, PA. If I recall correctly, it was located near what was then the Sheraton Hotel, which stood on a hill. Today, the building (located roughly behind the WalMart) is used for something else and, of course, the ski slope isn't there anymore.

Also, another lost ski area is Mt. Run, which was located near Mt. Jackson, VA and operated for a few years in the 1970s.

When I was looking at a place near 7 Springs, on White Mountain" the owner had a trial map of the mountain, and I guess there used to be ski area there. On Pritts Distilery Rd behind 7... about 10 min away

My sister's husband skied White Mountain back in the late 60's/early 70's. You can see the site of it from the Lost Girl trail where the 'future' Western Territory sign is. I recall riding up Pritts Distillery road in the early 80's and seeing the remains of lifts - ropetows, I think, although the memory is a wee bit fuzzy now.