Laserfiche WebLink
- • • <br />i <br />~ Grand Junction Pipc <br />' Surficial Geology {m•cstigation, Bean Ranch Road, Gravel Pit, Whilewater, CO <br />Februan 18. 1998 Page 2 <br />1 <br />This general arcs appears to exhibit relatively simple structural geology, primarily associated with the gentle east <br />' northeast dip of the beds. <br />Seismic events have occurred in the Grand Valley and areas south of this site. In general, these events were <br />evaluated as having Richter Magnitudes up to and including 4.4, with no reported damages. Based upon records <br />in Lincoln DeVore's libran, the closest rccendv active fault of the area has been located in a cut of US Highway <br />50 near the center of the north halCof Section 35, Township 4S, Range 3E, approximatel}• 10 miles from this <br />~ site. <br />SITE GEOLOGY <br />' This particular tract is underlain by the Mancos Shale Formation of Cretaceous Age. The Maness Shale is <br />considcral to be bedrock in this area. Basal upon structural geology mapping in this arcs, it is bclicvcd the bast <br />' of the Mancos Shale is near the Oow line of Indian Creek, Lo the southwest of this site. The Mancos Shale is <br />bclicvcd to be approzimatelc 120 to l50 Cce[ thick in this area. The Mancos Shale in this lower portion, <br />immcdiatef`• above the Dakota Formation, amtains significant developments of silt and sand. The Mancos Shale <br />is garcrallc fractured often to the point of being fissured and may eshlbit significant vertical permeability along <br />^ these fractures and some horizontal permeability along the siltstone and sandstone beds. <br />The su~cial soils on this site consist of a coarse grained, sandy, gravelly cobble which is alluvial in origin and <br />' may be interbedded with or part of ancient debris fan deposits originating on Grand Mcsa, to [hc east. The <br />gravels and cobbles arc primarily rvcll rounded, basaltic cobbles which arc derived from the upper basalt rocks <br />' on Grand Mesa and arc bclicvcd to correlate with the Pre-Bull Lakc Quatcmary deposit mapped by Yeend (U.S. <br />' G.S. 1969). This coarse grained gravel and cobble is the deposit to be exVacled from this pit. <br />GROUND WATER <br />' Some ground water ma}• be present beneath the alluvial gravels and cobbles. This water would be a seasonal, <br />perched rvatcr table on top of the Mancos Shale. Due to thegeometn of this ridge, it is believed any vvalers in <br />' the gravel and wbble would originate from snow melt or intense periods of precipitation. It is bclicvcd that any <br />perched rratcr which would develop on this ridge would be rather thin and would rapidly drain away. <br />A true ground water can often times be encountered in the louver sandstones of the Dakota Formation and <br />' undcrl~ ing sands within the Burro Canyon and Summcr•illc Formations. The upper member of the Dakota <br />Formation is bclicvcd to be 120 to I i0 feet below the present ground surface at this site. It is reported that some <br />rclaticcly shallow wells hate been drilled in this area. In addition, shallow springs are known to exist in the <br />t Indian Creek drainage. vvcst of the Bean Ranch Homestead, southwest oC this site. It is not known if these <br />springs or vvclls actually penetrate mto we aquifers or if these waters are just the result of accumulations m the <br />Indian Crcck alluvium. <br />SURFACE WATER <br />' The tract is located at the top of a ridge lino. Drainage in this arcs is generally off the properh to the north, west <br />and cast The mined areas bclrvicen this srtc and Highway 50 arc quilt Oat and probably do not contribute <br />1 <br />