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<br />oLittleton
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<br />
<br />Limit Of/
<br />Mapped
<br />Area
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<br />o
<br />I
<br />o
<br />
<br />1 2MILES
<br />I I
<br />2 3 KILOMETERS
<br />
<br />EXPLANATION
<br />t4880- WAlER-TABLE ALTITUDE-
<br />Interval is 10 feet Datumis
<br />sealevel. Arrows show
<br />direction of ground-water
<br />movement
<br />
<br />Figure 4. The water table between
<br />Fort Lupton and Platteville slopes
<br />down the valley and toward the
<br />South Platte River (Hurr, Schneider,
<br />and others, 1972),
<br />
<br />Work is in progress to expand the
<br />Fomprehensive mapping of the shallow
<br />aquifers into the area north of the
<br />Denver metropolitan area, Planned
<br />products include I :50,000-scale maps
<br />
<br />
<br />EXPLANATION
<br />-40-- UNE OF EQUAL
<br />SEDIMENT
<br />TIllCKNESS~
<br />Interval 20 feet
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<br />o
<br />I
<br />o
<br />
<br />1
<br />,
<br />2
<br />
<br />2 MILES
<br />,
<br />,
<br />3 KILOMETERS
<br />
<br />Figure 3. Thick unconsolidated
<br />sediments extend along a paleovalley
<br />cut in the bedrock surface (Stollar, 1969),
<br />
<br />of (I) the thickness of the unconsoli-
<br />dated sediments, (2) the paleotopogra-
<br />phy of the buried bedrock surface,
<br />(3) the altitude of the water table and
<br />direction of ground-water movement,
<br />(4) the saturated thickness of the
<br />shallow aquifers, and (5) the depth
<br />to ground water,
<br />
<br />As of July 1998, data for about
<br />11,000 wells and test holes were com-
<br />piled, checked, and interpreted to pro-
<br />duce a data base defining the thickness
<br />of the unconsolidated sediments and
<br />the altitude of the water table in the
<br />1,780-square-mile area. Data have been
<br />plotted and contoured at I :24,000 scale
<br />to produce preliminary maps showing
<br />thickness of unconsolidated sediments
<br />and altitude of the water table, The
<br />maps have been scanned to produce
<br />ArcINFO coverages that are being
<br />checked and attributed prior to use
<br />in preparation of the paleotopography,
<br />saturated thickness, and depth-to-water
<br />maps,
<br />
<br />Results of mapping the thickness
<br />of the unconsolidated sediments indi-
<br />cate that the alluvium in the principal
<br />stream valleys continues to thicken
<br />in the downstream direction between
<br />Brighton and Greeley, Thick sediments
<br />also are present along paleovalleys in
<br />
<br />various parts of the area of ongoing
<br />mapping, For example, in the area
<br />northeast of Fort Collins, thick sedi-
<br />ments define a paleovalley first mapped
<br />by Stollar (1969) in an area of rolling
<br />topography having no natural stream
<br />channels (fig. 3), Unconsolidated sedi-
<br />ments are 0 to 40 feet thick beyond the
<br />northward-trending paleovalley; sedi-
<br />ments are as much as 80 to 100 feet
<br />thick within the paleovalley,
<br />
<br />Preliminary results of mapping the
<br />altitude of the water table are in general
<br />agreement with previous mapping avail-
<br />able for parts of the area, For example,
<br />in the South Platte River Valley near
<br />,Platteville (fig. 4), Hurr, Schneider, and
<br />others (1972) indicated that the altitude
<br />of the water table was higher near the
<br />margins of the valley and lower near the
<br />South Platte River, Hurr and others
<br />(1975) indicated that ground-water
<br />flow is strongly affected by ground-
<br />water recharge, which occurs over the
<br />area of the aquifer from infiltration of
<br />irrigation water, rain, and snowmelt,
<br />Ground water flows from heavily irri-
<br />gated areas near the margins of the val-
<br />ley toward the South Platte River, which
<br />serves as a drain that controls the alti-
<br />tude of the water table near the river,
<br />The direction of ground-water move-
<br />ment is thus down the valley and toward
<br />the river, as indicated by the arrows in
<br />figure 4,
<br />
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