Grandmother's Rock, an old name of unknown origin, is a small outcrop of exposed limestone from the Oxwich Head and Clifton Down formations, in the undulating farmland east of Bristol, crossed by a stream which forms a waterfall, cascades and pools, all surrounded by a patch of moist woodland harbouring a good selection of wildflowers, mosses and lichens. The rock was quarried several centuries ago, resulting in vertical cliffs and residual boulders, while a ruined limekiln also survives from this period, used to heat the excavated stone to produce quicklime.
The limestone is from the Lower Carboniferous period, one of three inliers in this part of South Gloucestershire, surrounded by more recent Mesozoic strata (mainly mudstone), all generally covered by soils, so the exposed rocks of the limestone are uncommon. The usual range of ancient woodland wildflowers grow amongst the trees, while one rarer species is found along the top of the cliffs - yellow star-of-Bethlehem, blooming in mid spring.
Grandmother's Rock is reached by a narrow track, unsuitable for vehicles, linking Oldbury Lane with Marshfield Lane, 2.5 miles northeast of Bitton; this crosses the (unnamed) stream about half way, just west of the quarry site. The stream flows less than 2 miles, originating from springs at the upper end of a valley between Frozen Hill and Hanging Hill to the east, and joining the River Boyd near Upton Cheyney. It tumbles over a 4 foot waterfall into a rock-lined pool then winds through the woods for 400 feet, bordered to the south by the mossy cliffs of the old quarry, up to 30 feet tall. A path follows the north side of the stream, past the ruined limekiln. Wildflowers are scattered throughout the woods, and in a meadow to the south.