Interim Geologic Map of the West Part of - Utah Geological Survey

Ma.0122.65.311.6AGESystem Series and StageQUATERNARYHolocenePleistocenePlioceneuppermiddlevarioussurficialdepositsand lavaflowsredisuum?PLATEMAP UNIT MAP SYMBOLTHICKNESSTECTONIC DEPOSITIONAL ENVIRONMENT DOMINANT ROCK TYPE AND WEATHERING PROFILE NOTESfeet (meters)SETTINGhigh-levelpediment alluvium?high-levelfan alluviumLong Hillbasin fillLate Tertiaryfan alluviumregolithic brecca? ? ?Q_Qb_Tb_QTrQTapTafQTafQThQTbxvariable3 (1) 20(6)STRATIGRAPHIC COLUMN100+(30+) 300+(90+)1000+(300+)0-60(0-18)Onset of basin-range extenstion andcollapse of western margin of ColoradoPlateau beginning about 17 Mabasin fill in faultboundedParowan andSevier Valleys, but erosiondominant on MarkaguntPlateau; basaltic andandesitic volcanismsand and gravel;basaltic and andesiticlava flows; regolithicbreccia is weatheringproduct of MarkaguntmegabrecciaNote: Stacking order of Tertiary volcanic andvolcaniclastic units is approximate because ofage overlap and age uncertainty; not all unitsare in contact as shown. Lithology of some unitsnot shown.16.023.028.433.9TERTIARYOligoceneMiocenelowerupperlowerbasin fillNeedles Range GroupMarkaguntmegabrecciaHarmony Hills TuffHaycockMountainTuffLimerockCanyonFormationBauersTuffMbr ofCondorCanyonFm.Leach Canyon Fm.Quichapa GroupBear Valley Formation, undivided (breccia, tuff)Lund Formationrhyolitic tuffBrian Head Formation(middle volcaniclastic unit)Mount Dutton Formation, alluvial facies (mafic block and ash flow)Wah Wah Springs FormationTvfTnTbhtTm (Ta)Tm (Td)Tm (Tbvs)Tm (Tbvt)Tm (Tl)Tm (Tdm)Tm (Ti)Tm (Tnw)Tm (Tbhv)TqhTrhm Tqcb TqTqlTlTbhvTmTnlTnwTbv (Tbvb, Tbvt)Td (Tdm)100+(30+)35 (11)290 (88)50 (15)100 (30)15-100(15-30)Isom Formation Ti 140-350 (42-110)0-200 (0-60)1000+(300+)0-40 (0-12) east400 (120) west (Red Hills)0-200 (0-60)100 (30)300 (100)120 (35)100 (30)150 (45)150 (45)400 (120)40 (12)100 (30)500 (150)1000+(300+)Development of intermontaine basins (Paleocene-Eocene) and uplift of western US (Eocene-Oligocene): uplift continues to present dayExplosive, calc-alkaline volcanism and caldera development insoutheast Nevada and adjacent Utah from about 30-14 Ma; onMarkagunt Plateau, local volcanism and formation of megabrecciafine grained basin filleastern BullValley MtnsCalientecalderacomplex(Trhm fromMarkaguntPlateau?)IndianPeakcalderacomplexTm - catastrophicgravity slidelocalvolcanic rockssource of ash-flow tufflocal volcanicrocks depositedin low-reliefriver and lakebasinsvolcanic highlands and intermontaine basinsTm - mostly Isom tufflava andminor strata of Brian Head,Wah Wah Springs, andmafic block and ash-flowtuff that forms anallochthonous yet mostlyintact sheetlocal volcaniclasticstrata and rhyolitic ashmoderately welded daciticash-flow tuffTrhm - unwelded rhyoliteash-flow tuffTqcb - welded rhyolite ashflowtuffunweldedrhyolite ash-flowtuffdensely welded trachydaciticash-flow tuff;(tufflava or rheomorphicash-flow tuff)moderately welded daciticash-flow tuffmoderately welded daciticash-flow tuffvolcaniclastic mudstone,siltstone, sandstone;micritic limestone;volcanic ash;chalcedonyTm - about 20 Ma (possibly 23 Ma ifTrhm postdates megabreccia)Iron Peak laccolith (Tip) 19.7 Maand associated dikes (Tipd, Timd)20 - 21 Ma22.03 MaTqcb 22.7 MaTrhm 22.8 Ma; not part of Quichapa Group23.8 Ma26 - 27 Ma27.9 Ma30 Maupper part is conglomeratic in Red Hills andnorthern Markagunt Plateauchalcedonyforms large landslidesuppermost intervalTcwt109 (33)mudstonethin conglomerate lacks volcanic clastslower Brian Head Fm. of Sable and Maldonado (1997b)Eocenewhite memberupper limestonemiddle intervallower limestoneTcwTcwmlTcwuTcwmTcwl440 (135)