The land at 262 Eliot St—and for some distance on either side—is glacial till and drumlin. Under the topsoil, it is a loose mixture of sand and small, rounded stones with occasional small pockets of clay. The back part, near the water line, is mostly all sand and that is why the well there is so good.
The original plan was to carve out a pond back there and of course line it, since the soil drains much too freely for it to hold water. The water line of that pond would be four feet or so above the level of the Broadmoor pond. Roger Williams tried to do this, without a pond liner, and ended up with a dry depression that was later filled in.
From the street on back, topsoil was built up, over 30 years, by spreading many hundreds of trailer loads of manure from nearby stables and, sometimes, wood chips, a practice that continues today. Rainwater drains from the back of the house and, particularly, from the flat roof above the addition, into a plastic pipe that extends underground about 80 yards behind the house, where it flows down the embankment around the garden. 