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TABLE 2. Description of Geologic Units Shown <br />• on Map 4 (from Tweto 1976). <br />Qa i Alluvium -Gravel, sand, silt, and clay in stream valleys anJ alluvial Lin, <br />Tbp ~ BROWNS PARK FORMATION (MIOCF.NEI ~ Fluvial sillstonc, clay+lunr. <br />anJ tongiomera te, loosely consolidaleJ culian sandstone. anJ vnlcmu <br />ash OoulJery in plates; conglomerate al base. Maximum thick ncs+ <br />'A00 fl 1610 nU <br />UPPIIR TER'f1ARY INTRUSIVE ROCKS IPLI(1CI'.N I'. ANU h110- <br />CFNE -<20 m.y.l -- Mainly porphyries of inlenneJia It anJ basalUr <br />compositions. Mainly in ElkheaJ Mountains <br />Dike or sill <br />J <br />~ KI I LANCE FORMA~1'ION (UPPER CREL\CF.OUS) Gray shale, hghl- <br />hrown sandstone, anJ a few coal beds. Thickness 1,000-1,500 fl l JOS- <br />457 m) <br />.Kls LEWIS SHALE (UPPER CRETACEOUS) -Dark-gray homogeneous <br />marine shale. Thickness 1,500-1,900 fl (457-580 m) <br />Kw , ~ Williams Fork Formation -Light-brown to white sandstone, gray sh;dr. <br />~ anJ rnal heJs. 'thickness 1,100-?,000 fl 13?5-610 m) <br />K~ Iles Formation Massive beds o! light-brawn lu while s;m Jslone anJ <br />inter beJJeJ gray shale anJ coal. 'Thickness 1,5011 (t (457 ml <br />~L_ ~~I h1AN('OS SIL\LF (UPPER AND LOWICR (~RI''I':\CEOUSI -Cray to <br />Jark-gray marine shale. Sandstone beds near lupt calclrcuus s;uulsllvlc <br />o(Upper Cretaceous Frontier Member J(If1-100 fl 190-I ?0 ml aho~r <br />• base, overlain by lJleJfea US Shall' %onl' l'liplV;Jl`OI to NlU ~rafa I'Urllla- <br />tlon; silver-gray siliceous shale of Lower ('retaccous Mowry Shale Mcnr <br />brr nl base. Thickness about 5,000 fl 1 I,5'S ml <br />7 <br />