Definitely sounds like the hut circles near the dam. There is an old track that leads into the reservoir over a submerged bridge. Occasionally in the drier years it's possible to walk across it !
The natural outcrop near Batworthy sounds like Kes Tor as Lubin says ! Did you see the natural rock basins on the summit ?
It's certainly an area rich in stones - Fernworthy has a stone circle and several rows as well as clusters of hut circles in the forestry. There's also a nice kist on the Northern side of the reservoir (near the lifebuoy).
There's definitely a special kind of rain on Dartmoor !!