A rock stream, or block stream, is an accumulation of boulders or angular blocks, fragments that have fallen from cliffs or ledges above. Rock streams are usually found at the head of a ravine or on a slope below a summit, where they may extend into a forest or ﬁll a valley ﬂoor. One well-known site can be found in the Blue Ridge Mountains of central Virginia, downslope from Black Rock Summit in Shenandoah National Park. The quartzite-block ﬁelds on the northeast and western slopes of the summit are randomly displayed, suggesting that they were scattered by rockfall. Arthur Bloom, in his book Geomorphology, describes the rock streams in the Appalachians as relict features— that is, formed in the past under much colder conditions, when glaciers were nearby. In a less common usage of the term, rock streams are distributed along with the mass of soil that slides over a summer-melted layer of permafrost, a process called soliﬂuction.