Surficial Geology of the Bull Run Mountain Natural Area

Surficial units, or deposits, are unconsolidated deposits of rock particles overlying the bedrock. Alluvium and glacial till are examples of surficial deposits. Glacial till is not a component of the area's surficial deposits because the effects of the glaciers did not reach this far south.

The Surficial units are:
Qa - Holocene - Fine grain alluvium in modern flood plain creeks

Qcf - Holocene and late Pleistocene - (10,000 years and older) Fine grain debris on outer slope of Bull Run Mountain

Qc - Holocene and late Pleistocene - Coarse boulders of quartzite, greenstone, and debris in mountain slopes and hollows

Source: Data modified from the geological map of Washington West quadrangle by Peter Lyttle and others that is in production.
USGS