City of Alexandria, Virginia Geologic Atlas of the City of Alexandria, Virginia and Vicinity – Plate 2E NW E GEOLOGIC CROSS SECTION E’ SE FEET NORTHWEST FEET Claremont FOUR MILE RUN 200 GT-112 200 191 Tcg by Anthony H. Fleming, 2015 173 Kpl Barcroft Kpb Park 150 151 150 Kpcv 89

Kpcc Kpcs 100 100 Qc Lucky BEVERLEY HILLS Reservoir Qs Run Charles Kpcg Qaf SHIRLEY HWY Barrett Woods Qa QUAKER LANE MOUNT IDA J-1 60 School 63 GT-42 55 GT-85 GT-185 Shirlington GT-62 50 Qa 48 50 47 POTOMAC YARDS 50 GT-68 GT-67 Qto Qcf Qt 45 44 Qt Arlandria Qcf 39 38 Qa 39 38 Four Mile Rte 1 GT-4 Qcf 30 31 32 Hume Lynhaven 30 Kpcc 30 28 s Qt 25 Run Park GT-136 Qcf Spring GT-117 OCi Kpcv Qto 20 17 15 F-3 Kpcv 16 af 11 Qto af Qa af Qto Kpcs Kpcc Kpcc Kpch Qs Qt 3 SL 0 Qe SL -3 -7 ? Qal Qto-c Kpcc org

-25

95% sand org Qto-c -38 -50 Kpch? -50 Kpcc Kpcc

58% total sand (96/164) -68 OCI Kpcs

-100 Ogu -100

35% sand Kpcv?

-120 Kpcc

-150 -149 -150

OCs Kpcs?

-200 -195 -200

RCSZ -250 -250

-300 -300

SEE PLATE 5 FOR EXPLANATION OF MAP UNITS VERTICAL EXAGGERATION 20X

1000 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 FEET EXPLANATION OF CROSS SECTION SYMBOLS: WATER WELL GEOTECHNICAL BORING SITES WATER LEVELS REPORTED IN WELLS OTHER SYMBOLS J-60 WELL ID NUMBER AND SURFACE ELEVATION GT-27 ID NUMBER AND HIGHEST AND GEOTECHNICAL BORINGS 250 222 (SOURCE: J-JOHNSTON; D-DARTON; F-FROELICH) SURFACE ELEVATION 47 SURFACE EXPOSURE. SOME EXCAVATIONS WATER LEVEL MEASURED IN WELL OR COINCIDE WITH GEOTECHNICAL BORING SITES WELL CASING CASED GEOTECHNICAL BORING COMPLETED 119 IN THE CAMERON VALLEY SAND (LOWER GRAVELLY ZONES IN THE OLD TOWN TERRACE 10% sand AQUIFER OF THE POTOMAC FORMATION) APPROXIMATE LATERAL AND REPORTED IN GEOTECHNICAL BORINGS % SAND IN 100-FT INTERVAL REPORTED VERTICAL EXTENT OF SITE BY FROELICH (1985) ALONG CROSS SECTION LINE ORGANIC ZONES REPORTED IN GEOTECHNICAL WATER LEVEL MEASURED IN 1976 FROM BORINGS FROM THE POTOMAC FORMATION, WATER LEVEL 132 WELL COMPLETED IN CAMERON VALLEY ORG QUATERNARY ALLUVIUM, AND OTHER SEDIMENTS. 195 SAND (JOHNSTON AND LARSON, 1977) 70% sand INCLUDES WOOD, PEAT, LIGNITE, LEAVES, DARK WELL SCREEN ORGANIC SILT, AND OTHER ORGANIC MATERIAL 147 WATER LEVEL BEDROCK SURFACE WATER LEVEL MEASURED IN WELL OR INTERSECTION WITH ANOTHER CROSS SECTION. REPORTED BEDROCK LITHOLOGY GEOTECHNICAL BORING COMPLETED IN MOUNT IDA CROSS SECTIONS ARE DISTINGUISHED BY NAME schist OTHER AQUIFERS. MAY REPRESENT A BOREHOLE IN BEDROCK AND COLOR-CODED SECTION LINES AND TITLES 210 COMPOSITE OR AVERAGE WATER LEVEL AT BOTTOM ELEVATION OF 147 GEOTECHNICAL SITES WITH MANY BORINGS BOTTOM ELEVATION 127 DEEPEST BORING

GEOLOGIC CROSS SECTION 2E– FOUR MILE RUN cross section. The specific location of the cross section is indicated and organic horizons in the Old Town terrace that are present only in impressive buried escarpment below Lynhaven (site GT-117), which Cross section 2E follows Four Mile Run Valley downstream from on Plate 1 by a blue section line. the subsurface and thus do not appear on Plate 5. appears to separate older and more deeply entrenched terrace Barcroft Park, in southern Arlington County, to the extreme northern sediments to the east from thinner and presumably younger terrace end of Potomac Yards, near George Washington Memorial Parkway The cross sections are intended to be used together with the The dominant physiographic feature is the deeply entrenched valley deposits to the west. The two prominent organic horizons reported in and the Potomac River. The section begins at the lowest bedrock geologic maps, particularly Plate 5, to illustrate the third dimension of of Four Mile Run, which is flanked by many large terraces. Some of the borings at site GT-117 are suggestive of major periods of non outcrop on Four Mile Run, and traces the regular eastward slope of the map units. Contacts between map units are approximately these terraces are graded to the massive Old Town terrace, which deposition and weathering(?), accompanied by long-term growth of the bedrock surface and the corresponding thickening of the located and, in the Potomac Formation, are typically gradational or occupies the eastern part of the section. vegetation. The deep channel below this site may be the same as or Potomac Formation and younger alluvial sediments. The view is transitional. The abundance of control points (surface exposures, connect with the deep channel seen much further to the south below northward along the section line, which locally bends to take in the wells, geotechnical sites) along the cross section provides a general The Four Mile Run section depicts the array of terraces and other Old Town, although a direct connection cannot be established from locations of nearby geotechnical boring sites, historical water wells, indication of the reliability of contact locations. Map units are depicted Quaternary deposits that flank Four Mile Run, as well as the sizable existing data. The substantial thickness of the Cameron Valley sand and other places of interest (e.g., Reservoir Woods, Hume Spring). using the same colors, patterns, and labels as on Plate 5, and the body of estuarine sediment at its mouth, most of which is now buried member (Kpcs - Kpcv) at the base of the Potomac Formation in this These features, and other sites of cultural, historical, and explanation of map units on Plate 5 serves as the legend. The beneath artificial fill. The section also illustrates some of the internal section is likely related to its location near the thalweg of the Four environmental interest. are indicated by labels and symbols along the section also depicts some bedrock units and several gravelly zones architecture of the northern end of the Old Town terrace, including the Mile Run bedrock valley (see Plate 3 and its expanded explanation).