Chestnut oak / mountain laurel forest with large chestnut oak tree (Quercus prinus) in foreground and evergreen mountain laurel leaves (Kalmia latifolia) in background.
Photographer: Gary FlemingMost of the few and scattered stands of Chestnut Oak / Mountain Laurel Forest in Rock Creek Park grow on hilltops, atop remnants of ancient river terraces consisting of cobbles, gravel and/or sand. These gravels and sands were deposited by a prehistoric river. Later, the land was lifted up by tectonic forces, leaving these deposits high and dry. Ecobit: Ridgetop River Terrace Riddle

The soils on these hilltops and convex upper slopes are among the driest in Rock Creek Park because they are exposed to wind and sun from all directions. Rainwater percolates quickly through the coarse soil on these high surfaces, leaching away basic elements like calcium and magnesium and creating an acidic soil. Only a few plants thrive here due to the challenging conditions, which is why the natural community appears to consist almost entirely of two plant species well-suited to dry acidic soils—chestnut oak and mountain laurel.