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.,...u, GEOLOGY
<br />.,.., rn rho State. North of Snntn Chu•a Greek rand along the
<br />vesfern edge of the coal field the fornultia{ is ~renee•rslly poorly es-
<br />)osed. 'flee fmwatiau is completely trultented by the erosion surface
<br />{t the hose of the Poison Canyon formation rat the northern limits of
<br />he coal field, bat. thickens to 1,70Q feet southeast of rho Spanish
<br />?eaks.
<br />South of the Spanish I'enks, where rocks of the Rutotl fot•mntion are
<br />.cell exposed, the formation has been divided into three ununmed
<br />members (11rocR1, Johnson, P',nrgle, rand others, 195i; 1Vood,.IDllnson,
<br />xnd Uixon, 1956; rand 11'ood, Jnhnsnn, and Mixon, i957, p. 2~1--25).
<br />Harbour and Dixon (t959, p. ~i58) also scpnrllted [he fm•mntion into
<br />three major units, boa tl+ese do Hat cm•respoud to the membee•s differ-
<br />ar:tinted iIt Lhe earlier reports. The folvnntion bras not been sub-
<br />divided elsewhere in the cool field, but. it generally consists of a thin
<br />basal conglomerate overlain 6y interbedded sandstone, siltstone, shale,
<br />rand many coat beds.
<br />The 6nsal conglmncrate is extremely variable in Athology Hurl
<br />thickness, and varies from siliceous granule to pebble cnnglomernte to
<br />silicified conglomeratic sluldstane beds. Color r,u•ies locally from
<br />~ruy, purple gray, rand olive green to buff. 1'he conglomerate rnnges
<br />in thickness ft•om n thin edge smilhenst of Trinidad to 25Q felt near
<br />~5tmlewnll. Plus basal unit consists of one to t.tu•ee ttI•sn 'to mnssire
<br />'cliff- or ledge-forming beds, the lower of which is generally rontot•m-
<br />iillle with the upl>erlnost fx~ds of the Vermejo formation. Bedding is
<br />~nsunlly ohscut•e, but lomlly crossbedding is distinct. The mnt.rix
<br />is composer! of fine to very com•se sand trains. (Zunrtz granules and
<br />both fresh nlld weatherer) feldspar granules nre scattered throughout
<br />the conglomeratic sandstone. Chert pebbles are found in the eastern
<br />)art of the cool field, nod pebbles of ryuat•tzite, granite, nod gneiss nre
<br />lomirulnt in ille x•cstrrn lnu•t. Grains and €rnnules nre nnguiar to
<br />16t•ounded, rand the pebbles nre subanguhu• to well ronnled, The
<br />onglomerntic unit is nsuully ve)y well cemented by silica; howevor,
<br />t n very few phlces it is extremely fri::ble.
<br />Ahovo the conglomerate is nn alternating segnenco of g{•llywnclre,
<br />knse, and gnsu•t~osa s:uxlstone with interbcrldcd siltstone, shale, rand
<br />nt. 5andsimlo heels nr~s light 1==ray !o boil', and n1v. thin lu~ddecl to
<br />SSiVe. Thicker beds ure conunonly cross sta•Id.i(ied, and They nre
<br />et:•llly lenticnlnr hat. mny he irrea;ular or parallel. Tho grains
<br />ge fmm vm~• line to medium size, Luf• aro coarse la~ally. (icYUns
<br />v Prow subnngulnr to subrouuded, well to poorly sorted, :uui most.
<br />of quartz lrilh fewer grants of white we:lthered feldspar, ferro-
<br />lcsi;m minerals, ,rant rock ft;Il;ments. The sand grrtins nre ce-
<br />ed by ralcilml c;n•bonale and cloy. Shale, soul siltstonu beds arc
<br />RESOURCES OF TRINIDAD COAL FIELOr COLORADO ;~,j
<br />• gray to black, rand most of the beds nre t bicker than the be~'svld-
<br />stone. 'fhe shale is mostly pinstic lmd nonfissile, rand its caltent. of
<br />silt., s:uld, and cnrbonnceous mnterini rnnges cYidely. Shala r:Tries
<br />front pure cln.ystoue thl•ouglt silty shale rand sha.ly siltstone into silt-
<br />stone, cold the cnrhonnceous shale may grade into itttpul•e coal nod
<br />then into pw•e cont. Coral beds Decor tllrongllont the formntiml rat
<br />Homy horizons (fig. `L9}; but Went the top nIe alol•e leuticulur, less
<br />iture, ;tact Less numertuus. trregrclnrly sbnpert irnnstoue co:lcretinns
<br />occur locally in t.ha shale. Local intrufornulfionnl angular uncon-
<br />formities nre common in the Itn{mI formation rand nI•e especially a'el!
<br />exlx>secl irl thn rniley of tiro Purgatoire Ricer.
<br />ROOH9 OF TERTIARY AC.E •
<br />roluox cexzoH roa~ArtoR
<br />North of the Spanish Peaks the Poison Cauyou formatinu (Hills,
<br />189fl} of Paleocene raga unconformnbly ol•erlies the Itatorr rl,lcl older
<br />tormntious. Hoverer, iu t.ho ceutrnl :uul sontlrern parts rat the coal
<br />hold rho upl)er beds of the I{atop foruuliion iuteltungue with, mld
<br />locally grade vertic:elly nncl l:lteraliy irNO, the, !Quest beds of the
<br />Poison Gmyal formation. !'bus rat roost pblces in rho ceutrnl rand
<br />southern taut of the field the contact LeM'een the forunttions is dif!'i-
<br />eult ro deternune, flow-ever, the position of the contncf. is ch;R11'll at
<br />the base of the lowermost-salndstone that. contslins nna•eathered glaius
<br />of pink feldslmr. Smulstale beds are generally co:user grained in,
<br />Pu:unr. 20-•Ynderlek cool txA In Rntnn fnrmntl¢n exposed to aan of nm¢Il ¢u11ei{nq
<br />rand unrnnforennlgp• nvrrlnln 6r lentleulnr ennMlotte. Along Color¢do [State ante 12
<br />norfn of P¢rgntolrc Rlrer mul Ynldce. Coln. Vbr Ix ~~..n~.....
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