Geological Exploration of the Southern Rock Creek Valley in DC: Washington, D.C., July 13, 1989

16 Pages·0.78 MB·English

by  James V. O'Connor(auth.)

Geological Exploration of the
Southern Rock Creek Valley in DC
Washington, D.C.
July t 3, t 989
Field Trip Guidebook T208
Leader: James ~ O'Connor
American Geophysical Union, Washington, D.C.
Copyright 1989 American Geophysical Union
2000 Florida Avenue N.W., Washington, D.C. 20009
ISBN: 0-87590-674-5
Printed in the United States of America
Rock Creek Park
DISTRICT OF COLUMBIA
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IGC FIELDGUIDE T-208: GEOLOGICAL EXPLORATION
OF THE SOUTHERN ROCK CREEK VALLEY IN DC
James V. O'Connor
University of the District of Columbia, Washington, DC
Rock Creek Park is a special place FIELD STOPS FOR SOUTHERN
for studying geology. Founded as the ROCK CREEK GEOLOGIC WALKABOUT
city park in 1890, Rock Creek Park
serves as an oasis in the urban STOP 1
environment. Rock Creek Valley is a WOODLEY STATION & NEIGHBORHOOD:
steep craggy Piedmont eroded zone This Metro station is one of the
where one can observe the bedrock, deepest in the system. This older
follow the evolution of the Fall section of the city lies at the
Zone,and measure the topographically crossroads of Conn. Avenue. and
isolated Coastal Plain gravels. Calvert St. just west of the Rock
Figure 1 is the map of the stops Creek Valley. Indiana limestone is
to observe the general geology. the period building stone in the
area. Most notable scenery from the
The Rock Creek Valley is a textbook corner is the mural of Marilyn Monroe.
for research on the early Paleozoic
history. Metasedimentary and igneous Walk west on Calvert to 28th
rocks reveal the marine and tectonic Each building has its own set of
stories of a proto-Atlantic Ocean. stones. Note the small outcrop of
Metamorphic mineralalogy is set in soil and saprolite between the old
folds, faults, and fracture systems. and new Sheraton.
Paleozoic tectonics is covered on The slope of Calvert Street shows a
the bluffs unconformable by gravels valley of a stream named 28th St.
of the Mesozoic and Cenozoic. Branch.
The Cretaceous ancestral Potomac Turn right or south on 28th St.
sediments are also reworked into the The Lebanon embassy occurs at the
lower elevation sediment deposits of beginning of this street and is
late Cenozoic age (Miocene ? constructed of Mississippian Age
Holocene). Figure 2 is a general fossiliferous Indiana limestone.
geology map of the District.
Rock Creek served as a field site for STOP 2
the 5th International Congress for WOODLEY RUN--A LOST STREAM:
Geologists in 1891. We will revisit The Shoreham Hotel recreation area
some of those same stops almost a and 28th street cover the old stream.
century later and follow in the foot The alley between the Oyster Elemen
steps of the early American pioneers: tary School playground and the She
W. J. McGee, N. H. Darton, A. Keith, raton Hotel mark the upper reaches.
G. Williams, and B. Willis. The cliff at the National Park
boundary zone marks the depth to
which the fill has been carried out.
A small schistose outcrop occurs on
the west side of the street.
Follow alongside the park1ands.
Pieces of the old cobblestone walk
still exist along the parkside of
Please NOTE: the road. Many homes and embassies
WATCH FOR poison ivy plants or roots along the northwest side are of
BE CAREFUL of the auto traffic along Potomac Bluestone. This local rock is
the roadside. blue when fresh but weathers to rust
Drivers will not expect you. browns becau~e of iron weathering in
SAMPLE COLLECTION is PROHIBITED garnet (Almandine). The rock is a
in our National Parks. metasedimentary unit of the
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Figure 2: General Geology Map of District of Columbia
13
N
.
c.:.
Coastal Plain
\
Unconsolidated Materials o ,
1 Artificial fill I
2 Alluvium &sand . ..
o "- ~
3 Riverterrace deposits
\-, :II
4 Upland gravel &sand . •c..
5 Calvert Formation
6 Aquia Formation (
~
7 Monmouth Formation
)
8 PotomacGrp (clay&siltfacies)
~.
9 PotomacGrp (sand & gravel fcs.) I.
..
Consolidated Rocks & Weathered J .., 0 2 3
•
Residuum Piedmont Plateau t' I
'/ miles
10 Kensington gneiss
~
11 Georgetown maficcomplex
~
12 Gm complex (ultramaficrocks)
13 Wissahickon Formation ~
(peliticschistfacies) .
14 Wissahickon Formation
(diamictite gneissfacies)
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STOP 4
Glenarm Series/ Wissahickon Group. C.C. Glover or MASS AVE BRIDGE
& A PIEDMONT STREAM VALLEY OVERVIEW:
STOP 3 This current bridge is the second
BEDROCK & ENGINEERING ART: structure to occupy the site. The
Normanstone Run is a small tribu first bridge (1901) was a culvert
tary to Rock Creek. It begins in a for the stream and a bike trail. The
storm water drain at Reno Road and current bridge ws built in the 1940s
is a true stream within the national to conform to the city street system
park boundary. This stream is and cross the valley of Rock Creek
controlled by both the street system (cost $507,000). The bridge is 23m
(bridges) and the joint patterns above the parkway. Views from the
(structural meanders) of the bedrock bridge illustrate the steepness and
itself. The local bedrock was used narrowness of a typical Piedmont
to construct the weir and overflow valley. This hole or creek valley
flush for the storm sewer system. was a major stumbling block to early
The normal longitudinal profile is city development. Once Rock Creek
interrupted by gravel slides and was bridged, development 'of north
artificial waterfalls. The steep west and trade with Georgetown
relief of this valley and associated blossomed. Every bridge built over
channel float are a result of down Rock Creek is architecturally
cutting of this stream through its different by choice. The US Army
Coastal Plain gravel cap to the bed Corps of Engineers until recently
rock. The V shaped gravel cap controlled all public works and ran
controls the local drainage as a the city. Earlier studies on the
divide. Wisconsin Ave is the east city water supply by the Corps
arm of this cap centered at Fort looked at and proposed a reservoir
Reno which is the city's highest dam where this bridge is. This site
elevation (420 feet or 103 meters). was not chosen but is rediscovered
and reported on every few decades.
There are three granite gneisses
observable in DC. They are a horn Mass Ave NW is known as Embassy Row.
blende-biotite gneiss, a biotite This street has many major religious
gneiss, and a biotite-muscovite houses of worship as seen from here.
gneiss. The origins of these three This bridge is named for Charles
gneisses is still debated but three Carroll Glover, a local wealthy
possibilities exist: 1. Indicate resident, pushed for the
change due to metamorphism, 2. Indi creation of Rock Creek Park, and
cate different magma pulses, 3. donated land for the site of the
Indicate different magma phases. National Cathedral at Mass & Wise.
Due to lack of critical outcrops, The southwest end of the bridge marks
the time relation of the three is Lovers Lane. This historic roadway
not debated. The mineralogical is now a gravel path but has a his
analysis differentiates three tory as part of the escape route for
distinct gneisses sometimes describ the 1814 burning of the capital. It
ed as metatonalites or meta-quartz also marks the vertical contact of
diorites. At the headwater pipe just the Coastal Plain terrace gravels
upstream, Georgetown metamafics are and the Piedmont bedrock. As you
in contact with the gneissic mate enter the trail watch for the hugh
rials. Gneiss is younger. Two varia quarry hole to the east and the
tions of the gneiss, possibly all roundish gravel pit excavation to
three, may be observed in this the west. This abandoned resource
streambed. Table 1 gives the mineral area is plotted on soil plate 6 in
analysis of this and other stops the DC Soil Survey.
for comparison.
Follow Lovers Lane to Dumbarton Run
Follow the park edge southeast
toward Mass. Ave.
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STOP 5 The recent crosstown water project
DUMBARTON OAKS-MONTROSE PARK cut a n~w tunnel along N Street
& the GEORGETOWN MAFIC COMPLEX: through Georgetown. Drilling data and
Just before the stream( Dumbarton cores define the east-west width of
Run),there is a large outcrop of the metamafic body under Georgetown.
saprolitized, chloritized schist. Dumbarton Run marks a major contact
The soil survey differentiates the between the metamorphosed ultra-basic,
schist (Nashaminy soils) from the basic, and semi-basic igneous activity.
gravels (Sassafras soils). Better Follow the Rock Creek path upstream or
and less weathered mafic units are north toward the Mass Ave Bridge.
found in the building stone wall of
Dumbarton Estate along the parklands STOP 6
which contrasts nicely with the MASS AVE or DUMBARTON QUARRY:
Potomac Bluestone wall along Lovers This is the second largest quarry
Lane. Seasonal springs occur in the in the parklands. This massive over
middle of Lovers Lane and the tar grown quarry has hornblende meta
patches in the street give testimony diorite on the north-northeastern
to this flow from the terrace facing wall and lighter metadiorite
bedrock interface. on the east facing back wall. The
contact shows the lighter diorite
Dumbarton Oaks was a private resi cutting the darker. Aplite and lam
dence built in 1801 for William H. prophyre dikes are common. These
Dorsey. This massive estate with its dikes vary in size but show flow
world reknowned landscape gardens and offset. The quarry face has well
and pools belonged to Mr. & Mrs developed joint patterns and minor
Robert Woods Bliss from 1920-1940. faults. Poison ivy and thickness of
In 1940 they donated the house and vegetation make this study possible
the sixteen acres grounds to Harvard only in the dead of winter. Photos
University and sold ,the back twenty in Fellows (1952) are a good alterna
seven acres of gardens and forest tive to viewing the structures. The
along Dumbarton Run to the National rock itself seems to have been used
Park Service for one dollar. The for the bridges, estates, and other
meeting to establish the charter for local construction.
the United Nations was held here in Follow trail north under Mass Avenue
1944. The engineering feats of the Look for the decay of the bridge.
outer public gardens (NPS) have fal How many stalactites are visible?
len into ruins in recent years but Note the thick dripstone deposit
the waterwheels to pump spring water along the trail. Can you find any
to the main house can still be obser stalagmites? There is a small vine
ved in two springhouse remains. covered quarry on the northwest side
of the bridge. This rock is the
Montrose Park was the 16 acre garden Kensington dioritic gneiss. It is
estate of mill owner Richard Parrott. highly jointed and here highly
He called his estate ELLERSLIE (1813). weathered. As you walk the flood
This site became parklands in 1911. plain picnic area, can you find
Outcrops along the Dumbarton Run any beaver evidence.
trail exhibit light and dark "ghosts" Junction of Parkway: Can you find
in the hornblende diorite. These the original ford? How has the river
ghosts-laden outcrops are very changed course?
evident halfway down the hill and
at the junction of the trail with
Rock Creek. The south bank of Dum
barton opposite the trail has massive
veins of milky quartz. These veins
are quite common in this area of the CAUTION: CROSS THE STREETS AT THE
Piedmont and some contain gold. CROSS WALKS ONLY!!!
This area is where the Lydecker RETRACE YOUR STEPS ACROSS THE BRIDGE
Tunnel that carries the city water ON THE EASTSIDE AND FOLLOW THE OLD
supply from Georgetown to McMillen QUARRY ROAD THAT LIES ALONG THE EAST
reservoirs runs under Rock Creek. BANK AND SOUTHEAST SIDE OF BRIDGE.
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STOP 7 railroad architect George S. Morison.
OUTCROPS AND CONTACTS: This bridge was one of the first uses
The CONN. AVE. or TAFT QUARRY of ornamental concrete and exposed
Three large outcrops occur from aggregates. The other major bridge
Waterside Drive to this spot along to the north is the Calvert St or
the parkway. First is the massive Duke Ellington Bridge which is made
intrusive at the retaining wall from Indiana limestone. It was built
(Waterside Drive). Second is the in 1935 and replaced a 1891 bridge
contact zone here. Third is a large built by the Rock Creek railroad.
aplite dike with a quartzite like Recent controversy surrounds the
core that lies between the two. This Calvert St bridge. Observe the new
strange aplite dike quarried out here higher metal picket fence. This is
is associated with isolated units in to prevent suicides. With height
a linear belt from here through the restrictions based on the Washington
park into Maryland. Three hypotheses Monument and Capitol, the Piedmont
are in vogue: metamorphosed chert, valley drop from the top of this
altered quartz vein, or reheated bridge had about seven jumps per year.
coarse pegmatite. The legal hassles of the fence on
Following the old road path upstream. an historic structure caused a minor
The TAFT Quarry or Conn. Ave. quarry community struggle. Now the suicides
lies on the southeast end of the Taft have spread to the other bridges we
Bridge below the Chinese Embassy. just saw- Conn and Mass Aves.
This is the largest abandoned quarry Suicide Cliffs are a special function
in the parklands. Overgrowth, urban of this city's geomorphology and laws.
disposal and urban safety provide Washington's new subway system METRO
hinderences to a good analysis of was built in segments. The red line
this bedrock. There is only a two runs under your feet. The old stable
month window for exploration. areas were the staging ground for
three separate construction contract
segments: Dupont north, Conn Ave to
Van Ness, and Rock Creek connector
STOP 8
tunnel. Vegetation scars on the west
OBSERVE DC TRANSPORTATION
valley wall show where the tunnel
HISTORY FROM STONE MONUMENTS
went into the hillside to create the
From this parking lot one observes
Woodley Station and areas north to
four historical types of urban
the UDC campus at Van Ness.The area
transportation and the accompaning
between the streetcar abutment and
engineering geology. The remnants of
stables is where the Dupont segment
horsepower, streetcar, auto, and
came out. A special cofferdam system
rapid transit are evident here.
was set up to divert Rock Creek and
The abandoned Edgewater Stables
connect the two major tunnel sections
which now serve the mounted park
under Rock Creek. Late 1970s
police unit,and the small red sand
hurricane related floods did tempo
stone or brownstone ( Mesozoic
rary damage as the cofferdams failed,
Culpeper Basin) abutments of the
but caused no great harm or delay to
original Woodley Bridge (east bank
the 1981 opening of the red line
of creek) allow you to fantasize
along this route.
about the horse and buggy days of
The National Park Service required a
country getaways. The high stone
special pre and post photographic
abutments (Piedmont Bluestone) on
assay of the small bridge here
the north side of the stables are
by the METRO construction groups.
the remains for the iron truss
Restoration costs and structural
bridge foundation. This streetcar
damage were assessed by this method.
line was the first to cross the Rock
The small Potomac bluestone house on
Creek valley and open the Conn Ave
the northeast side of the bridge was
corridor for development via the
part of a brief water quality instru
Chevy Chase line to Chevy Chase
mentation study conducted by the US
Circle (1888). Auto traffic was
Geological Survey (1971).
carried by the Taft or Conn. Ave
Bridge. Started in 1897 and completed
in 1907, this million dollar bridge Carefully cross Beach Drive.
was the first great masonry bridge Proceed along the bike trail to the
in DC. It was designed by the great cafeteria at the Zoo. LUNCHBREAK
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Alternate trail on the east bank whole area is off limits unless
maybe used but is less maintained. special permission is obtained from
the Smithsonian or US Fish &
STOP 8B Wildlife Service.
GEOLOGICAL FOUNDATIONS OF
THE NATIONAL ZOOLOGICAL PARK Climb old Adams Mill Road.
(Smithsonian Institution) Numerous small dimension stone
The zoo was established by Congress quarries exist on the northside of
in 1889 and is now celabrating its roadway. Recent repaving of this
centennial year. The zoo was built roadway covered over the excellent
on the hillsides and plateaus of cobblestone gutter on the southside.
this classic Piedmont valley. The retaining wall was constructed
Many of the animals were gifts from of local stone and the quarry is in
other nations. Recently major reno the woods at the southeast side of
vations blending with the not~on the tunnel. The Rock Creek -Beach
that animals have rights and that Drive tunnel is twenty five years
zoos should duplicate the natural old. Three parallel lines of drill
habitat have brought many new buil cores (19 data points) indicate a
dings and landscape designs to this fault from the change in rock type.
zoo. The major original design for While the cores are no longer avail
the grounds was a Frederick Law able, the engineering records have
Olmstead project and the new walkway been turned into an urban geology
was done in his honor. Beaver Valley cross section lab (Bacon/O'Connor).
has a unique artificial rock that The tall gabion wall exposed on the
blends into the natural scenery. valley edge near the zoo gates con
Back track to the southern ford trols erosion and dumping. Before
along the east bank of Rock Creek. convertion to a community playground
and gardens, this area was a cemetary.
STOP 9
JOHN QUINCY ADAMS MILL SITE STOP 10
The southern entrance to the zoo ZOO GATES AS RESEARCH WALL
along Beach Drive looks grim today. & DARTON'S THRUST FAULT
Before the auto tunnel was opened in Here at Adams Mill Road and the
1965, this roadway was the main administration entrance gate for
commuter road. Newspaper acounts the zoo are two geologic wonders.
indicate that many cars were washed The gateposts are a long term
downstream when trying to cross the research study, and the thrust
creek during high water especially fault is preserved for observation
in summer flash floods. This major though highly weathered. All the
ford or concrete apron helped the original entrance gates for the Zoo
auto shocks avoid the normal river and old National Bureau of Standards
gravels. Where old Beach Drive inter were constructed of local building
sects old Adams Mill Road was the stones from the Piedmont with Aquia
location of the mill. This brick sandstone (Potomac Group- K Age.)
structure was build about 1800 for caprock. The gates were oriented by
Benjamin Stoddard, the first Secre compass direction and emplaced with
tary of the Navy and sold to J.Q. foliation both horizontal and ver
Adams about 1825. The building has tical to the observer. The art and
totally disappeared. On the west architecture of these gates was
bank is a medium size abandoned designed as a long range research
quarry. There is a major shear zone project to test the weathering
on the northside of the cliff. characteristics of local stone
Slickensides and mineralization (Bassler,1940). Only two other sets
show a variety of movements and of gates exist today: Conn. Ave.
splays. The protected Hays Spring entrance to zoo, and the Conn Ave/
occurs in this area and is a joint Upton St gates now for Intelsat
system spring combined with a buried complex. Which stone is the most
stream which was filled in and weathered? Which side is in the
sewered for Cathedral Ave. on the worst shape? Look for yourself and
bluff above•. This spring area choose the best answer!
contains the only endangered species With the construction of the roads
in DC. The species is an isopod. The and neighborhoods around the zoo,
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