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Stratigraphy (Exhibit H and M) <br />Precambrian <br />The oldest rock outcropping in the vicinity is the exposed eastern flank <br />of the Wet Mountains directly to the west of the General Area. <br />The exposed metamorphic complex is a crystalline rock mixture of <br />gneiss and s~:hists intruded by granites. <br />Pierre Shale <br />Outcropping approximately two miles east of the General Area and <br />within the Cr~andler ridge of the Wet Mountains is the non-coal bearing <br />Pierre Shale. The USGS describes this unit as an "olive-gray, clayey, <br />silty and sandy shale that contains beintonite beds and marine fossils <br />throughout". The Pierre Shale is characterized by very low hydraulic <br />conductivity and is considered to be an impermeable basal <br />unit relative to the regional ground water system. At the top of the <br />Pierre is a sequence of thick, interbedded, fine-grained sandstones and <br />mudstones. These sediments are a prodeltaic sequence transgressing <br />on the "Pierre" sea to the east. Total thickness is projected as 3,900 <br />feet. <br /> <br />Trinidad Sandstone <br />Overlying the Pierre Shale and outcropping in the Chandler Ridge are <br />sandstone beds of the Trinidad Formation. The basal contact is <br />transitional in nature, indicating a depositional change from the <br />prodeltaic sediments of the upper Pierre to the delta from deposits of <br />the lower Trinidad. Sediments of the lower Trinidad are generally very <br />fine to fine grained, clay rich, buff to yellow sandstones with thin <br />mudstone laminate. Overlying these delta front deposits are tributary <br />channel sanci deposits of the upper Trinidad. These sands are <br />generally-fine to medium grained and light gray to buff in color. Total <br />Trinidad thickness ranges from 40 to 50 feet. <br />Vermejo Formation <br />Overlying the delta deposits of the Trinidad are the complexly <br />interbedded mudstones, siltstones ,sandstones and coals of the <br />Vermejo Formation. These sediments were part of a vast fluvial delta <br />plain sequence prograding eastward on the "Trinidad Delta." <br />Differential compaction of the accumulating sediments and regional <br />subsidence concurrent with deposition allowed moderate thicknesses of <br />coal to devellop in river swamps of the delta plain. <br />The Vermejo Formation is the coal bearing unit of interest in the <br />Northfield PE~rmit Area. In ascending order, coal horizons of <br />significance include the Rockvale, Canon City, Ocean Wave, Royal <br />Gorge, Chandler, Wolf Park and Brookside. Stratigraphic relationships <br />2.04-9 Revised 5/01/07 <br />