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The site general geology was described in a preliminary geologic evaluation report <br /> prepared by F.M. Fox Associates, Incl at the time of original DMG permitting in <br /> 1978. A copy of this document is included as Attachment A for reference. The site is <br /> underlain by a thin veneer of hillside colluvium(up to several feet), which is in turn <br /> underlain by metamorphic rocks varying from schist to granitic gneiss. The <br /> colluvium is Pleistocene to Holocene(Recent) and the bedrock is Precambrian. <br /> Pleistocene alluvium reportedly exists at the extreme western edge of the site,but is <br /> not of interest because it is west of the active mining operations. <br /> The Fox report appears to be based on the Reconnaissance Geologic Map of the Pine <br /> Quadrangle(1:24,000)2. A copy of an excerpt from that map showing the project site <br /> area is included as Attachment B to this report. The geologic information included in <br /> this reference confirms bedrock consisting of migmatitic biotite gneiss with biotite <br /> schist, granitic gneiss, and amphibolite.General geologic structure mapped near the <br /> quarry includes north to northwesterly striking,easterly to northeasterly dipping <br /> foliation and metamorphic compositional layering generally parallel to the foliation. <br /> Dips are shallow to moderately steeply dipping, and generally into the hillside at the <br /> quarry site. <br /> With respect to the four summary and conclusion items included in the Fox report, <br /> Brierley Associates offers the following updated comments: <br /> 1. We concur that the site bedrock is composed of compositionally layered <br /> metamorphic rocks that include interlayered biotite gneiss,biotite schist, <br /> amphibolite and granitic gneiss. These rocks are commonly referred to as the <br /> "Idaho Springs Formation" as indicated in the Fox Report,but are referred to as <br /> undifferentiated metamorphic rocks of Precambrian Age(1,700— 1,800 m.y.) on <br /> the Geologic Map of Colorado.3 In addition,because of the migmatitic texture of <br /> the predominant gneissic rocks, irregular bodies of rock composed of granitic <br /> lithology also occur within the layered metamorphic rock types. <br /> 2. We concur that metamorphic foliation is developed parallel to well-developed <br /> metamorphic layering, which generally dips moderately steeply into the hillside. <br /> The Fox report indicates an easterly dip. Our mapping efforts indicate an average <br /> northeasterly dip as discussed further below. <br /> 3. We concur that the rocks presently exposed do not exhibit any prominent faulting. <br /> We do find there to be mappable jointing in the rock mass,in addition to the <br /> foliation jointing. One could argue this jointing is not"prominent"in that it is not <br /> continuous over hundreds of feet, there are jointing trends continuous over tens of <br /> feet that could affect slope stability as discussed further below. <br /> Preliminary Geologic Evaluation of a'Proposed Aggregate Quarry Site at Shaffer's Crossing,Jefferson <br /> County, Colorado;F.M.Fox&Associates,lnc.;May 5, 1978. <br /> 2 Reconnaissance Geologic Map of the Pine Quadrangle,Jefferson County,Colorado;by Bruce Bryant; <br /> Miscellaneous Field Studies Map MF-598;U.S. Geological Survey; 1974. <br /> 3 Geologic Map of Colorado;Compiled by Ogden Tweto;U.S. Geological Survey(In Cooperation with <br /> The Geological Survey of Colorado); 1979. <br /> JC 00770 <br /> PetersonIEt Creek <br />