Laserfiche WebLink
QUATEKNARY GEOLOGY uF TIIC i101'C IIKItiS-I'AUN1A kl;S i~:l<VUIK AH L''A <br />DELTA AND GUNNLSUN I:UU N't'l l:S, CO LU K>\Uu <br />CENtkAL <br />The Hotchkiss-Paania Reservoir area includes the Nurcl, Furk Gunnison Rtvur <br />and its tributaries Sn northwestern Gunnison anJ eastern Uelta Counties. Six <br />contiguous 7~-minute quadrangles arc in tLc ar,a studied; they are Cray Resrrvulr, <br />Bowie, Somerset, Paonia Reservoir, Hotchkiss, anJ 1'..unia. fire quaternary geology <br />of 'each quadrangle is mapped at 1:2~~,000 and represents the general geologic ev~- <br />lution of Che area during [he latest pcriuJ of g,oulogic time. Maps of yuateruary <br />geology were prepared to define young geologic units with cumnx+n characteristics <br />and to identify potentially hazardous geologic conditions. 'fire geoluKic relati~n- <br />ships of the Quaternary depicted on these maps ace useJ as a technical basis fur <br />[he coupilatlon and interpretation of the comp:~nion geologic-hacard cups. <br />MAP UNLTS <br />The general geologic setting of [his area is relatively simple: flat-lying <br />Czetaceoua and Tertiary strata locally intruded by igneous rocks. 'f he sequence <br />vas sculpted during the Late Tertiary and Quaternary by erosional pro~:esses that <br />forced the present mesa and mountain landscape. Various chin Quaternary deposits, <br />probably related to glacial stages, suggest th.tt fluvial and mass-wasting activities <br />were the dominate geomorphic processes in the Cunwtion of the present landscape. <br />Glacial, colluvial, and alluvial Quaternary deposits are shown ott the maps and <br />:scribed in the Explanation of Map Units. Glacial deposits include these surficial <br />.airs which wer,: transported and deposited by ice naveuient ur by glacial mcltwaters. <br />Mdse of these Jepusits probably arc Late Wisconsin, altltouglt o1Jer deposits may he <br />• present locally. Alluvial deposits arc clay to huulJur-size material transported <br />and Deposited by running water (fluvial pn~ce~>se~:). Aleh~~ul•,h age of the alluvial <br />deposits is unknown, the map units arc placed iu a geue riL time Crawewurk basad <br />upon available geomorphic evidence. Age and correlation of specific deposits <br />within the alluvial gravels (Qag) are basoJ un soil D welupmenr, in-place weathering <br />of igneous-rock fragments, and position above modern streams. Uivursu litholugy <br />of the deposits, caused by extreme variatiunv in local source areas, nuked definite <br />correlations difficult and thus those inDic.~toJ are only .~pproxinute. ADditionally <br />more than one d.:positional cycle, as indicated by sevcr.il retrace levels, nwy be <br />included in a syecific mop unit. Culluvi;iL uepuwits gcnw ally arc uncun;;uliJatcJ <br />soil and/or rock detritus depusi[ed chie:ly Ly mass-casting processes. Relative <br />age of these deposits is noted by subscriv's after the map symhul. Subscripts <br />range from 1 to 1. Deposits with subscript 1 Formed probably during the Holocene; <br />whereas 2 and 3 may represent Wlseunsin dcpu~:its. Ln aJDiciun to the Quaternary <br />deposits, exposed bedrock is indicated on the map. where necussory the bedrock <br />symbols as described in [he Explanation of ~~!:L-Units .ine in parentheses following <br />the map symbol for the. Quaternary deposit <br />• F'-30 <br />Rev. 1: b-18-81 <br />