_PERMIT FILE - M1997053 ‎(36)‎

• Permit No: M1997053
• IBM Index Class Name: Permit File
• Section_Exhibit Name: EXHIBIT I SOILS INFORMATION
• Media Type: D
• Archive: No

1
' Grand Junction Pipe
Surficial Geology Investigation, Proposed Clifton Water Pit,34 & E 1/4 Roads, Clifton, CO
March 24, 1997 Page 2
' SITE GEOLOGY
' The tract and this general portion of the Grand Valley is underlain by the Mancos Shale Formation, of
Cretaceous Age. The depth to the Mancos Shale has not been determined by personnel of Grand Junction
Lincoln DeVore. It is believed ltte Mancos Shale Formation will be encountered approximately 20 to 30 feet
' below the present ground surface across this tract. The Mancos Shale beneath this tract is the lower portion of
the formation and contains thin interbcds of sillstone and sandstone. The Mancos Shale is normally described
as a dark grcc. moderately thin bedded to laminated claystone and shale. Silty and sandy strata are present
' throughout the shale and are expected in the formation beneath this site. The Mancos Shale is considered to be
the competent bedrock in this part of the Grand Valley.
t The tract is located between the Uncompahgre Uplift to the southwest and the Pittance Basin structural feature
to the northeast. The bedding planes of the Mancos Shale dip to the north, northeast with a gentle slope of
approximatch G to 10 degrees. In general, the geologic structure beneath this site and in this portion of the
t Grand Vallee is relatively uncomplicated
The Mancos Shale is exposed on the small bluff on the south side of the river. This bluff is the northern most
expression of the geographic feature referred to as East Orchard Mesa. The top of this small bluff represents
' a former depositional terrace of the Ancient Colorado River.
The surface soils on this site consist of 4 to 7 feel of fine grained, unconsolidated silty sands.sandy silts and
' occasional silt\clays. These fine grained soils arc stratified. These upper soils are composed of overbank flood
floe deposits from the Colorado Rivcr,which intermingle with clayey deposits from ancient muciflows which
originated in the Bookcliffs to the north and northeast. It is anticipated the surface soils will be removed and
' stockpiled for reclamation purposes.
It is belie%cd that appro.ximatcfy 15 to 25 feet of coarse grained sandy gravels and cobbles are present on this
site. These coarse grained gravels and cobbles represent an ancient bed load of the Colorado Rivcr and are
composed mostly of medium to fine grained granitic rocks. Some volcanic rocks and occasional metamorphic
rocks have been encountered in these deposits. These coarse grained gravels and cobbles all originate in the
' upper reaches of the present Colorado River drainage. Some cobbles and small boulders up to 19 to 24 inches
indiameter ha%c been encountered in this deposit, particularly near the base of the alluvial soils. The relali%c
amounts of silts. sands and small gravels is erratic throughout this terrace deposit.
' GROUNDWATER
Actual ground %%ater measurements have not been made on this silt. Based upon general information in this
' area.to include exploration pits immediately north and west of this site. it is believed the ground water Icvel will
stabdi/c at approximate]%5 feel below, the present ground surface. The Icvel of the ground water will be subject
to some fluctuation,depending on irrigation practices to the north. northeast and the actual free water surface
' of the Colorado River to the cast.
The ground water table in this area is a perched water table.continualh fed by the Colorado River and valley
' wide irrigation practices. It is believed the general direction of subsurface flow on this site is generalh toward
the southwest to west direction.