The scouring force of infrequent floods along the Potomac River has created a unique habitat for special plants at Great Falls in Montgomery County.

Here the National Park Service has joined with the Maryland Natural Heritage Program to monitor and protect rare species like yellow nailwort. This rocky streamside, “barren” specialist flower in midsummer. Disjunct from Missouri and Oklahoma, it is Endangered in Maryland.

Many other rare plants live along the stretch between Great Falls and Little Falls, and two rare mussel species live in these waters.

Severe storms can cause the Potomac to increase to 40 times average flows, although such storms may occur only once or twice in 50 years. These floods carve the spectacular cliffs, and scour plants and soil from the floodplain. The barrens then slowly revert to forest until the next big storm.