Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

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Figure 39. Summary of Rio Grande rift architecture and location of Tertiary and Quaternay volcanic ash localities. Maysville quadrangle location shown with white rectangle. See text for sources of map information. The complex structural relations in the Maysville quadrangle indicate the presence of a major N70°W-trending, transverse fault, the Salida-Maysville fault. We suggest in this report that the Villa Grove accommodation zone of Chapin and Cather (1994) is the southern end of a broad, transverse boundary zone between the San Luis 170
graben and the Upper Arkansas Valley graben. It extends from Villa Grove in the upper San Luis Valley to the Salida area and is bounded on the north by the west-northwesttrending Salida-Maysville fault (fig. 39). Such an interpretation is favored because the symmetry of the rift shoulder uplifts does not abruptly change but is more of a transition across this broad 20 mi wide area. On the west side of the rift, the Proterozoic rocks in the core of the Sawatch Range extend southward (partially under Tertiary volcanic rock cover) to Mineral Hot Springs where these rocks terminate at the north end of the San Luis Valley. On the east side of the rift, the Proterozoic rocks in the core of the Sangre de Cristo Range continue northward to Poncha Springs, where they terminate at the south end of the Upper Arkansas Valley. Thus the asymmetric rift shoulder uplifts overlap for about a 20 mile wide area. Therefore a more inclusive name for this complex zone is the Poncha Springs-Villa Grove accommodation zone (see fig. 5). Observations presented in this report suggest two and possibly four or more volcanic ash beds are present in the South Arkansas graben sequence (Td2). Additional volcanic ash beds have been reported in the Upper Arkansas graben sequence (Td). Table 4 provides a compilation of all Miocene and Pliocene volcanic ash localities that have been identified in the southern part of the Upper Arkansas graben and the South Arkansas graben. Nine localities of volcanic ash are identified in the Dry Union Formation (Td and Td2) and three localities of volcanic ash are in Quaternary deposits (fig. 39). Multiple ash beds are reported at four of the Dry Union Formation ash localities. Basic characteristics of the ashes including thickness, presence and character of glass, mineralogy of primary crystal fragments, and degree of contamination may provide information that could be used to correlate the different localities. More advanced techniques including tephrochronology and glass and mineral chemistry may help to confirm correlations and ultimately provide absolute ages on specific volcanic ashes. Consequently, the volcanic ash beds in the Dry Union Formation are suggested to be important time-stratigraphic markers that will be useful in recognizing and separating the different stratigraphic sequences in the different Dry Union Formation structural domains and providing absolute age constraints on inception of rift-related faulting and sedimentation. 171
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OPEN-FILE REPORT 06-10 Geologic Map
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TABLE OF CONTENTS Introduction…
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mylonitic, augen textures………
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INTRODUCTION LOCATION AND ACCESS Th
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SAWATCH RANGE RIFT-SHOULDER UPLIFT
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of the South Arkansas River (subseq
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EXPLANATION Rio Grande Rift Neogene
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in descriptions of the geologic uni
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During the Early and Middle Paleozo
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Mountains, and White River uplifts
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field are the largest remnants of t
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Figure 5. Detailed geologic-structu
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with the Colorado mineral belt (Boo
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Shannon, 2005). Widmann and others
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the Upper Arkansas graben (fig. 5)
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15-minute quadrangle, which is adja
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etween the northern and southern se
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on U.S. Forest Service color aerial
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We use fractional map units on the
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Qpt Pinedale till, undivided (late
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weathered, but Mount Princeton quar
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stratified, matrix-supported, bould
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as rockfalls, rock avalanches, rock
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stream-channel deposits of all pere
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Figure 10. View west up South Arkan
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Figure 11. View west up South Arkan
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valley near the eastern map boundar
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lithologies are variable and depend
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Arkansas River in parts of Redman C
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angular to subangular. Deposits gen
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elations, age constraints from foss
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elated to the inferred Squaw Creek
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Figure 14. Crude bedding in coarse
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microcline, and muscovite. The latt
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Volcanic Ash Figure 17. View of eas
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Figure 18. Close-up view of intense
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The western zone of brecciated Pale
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Tr Rhyolite dikes (early to late Ol
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as the overall N47°E trend of the
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One age determination on the rhyoli
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northwest-trending fault. Thus, fie
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on the North Fork leucogranite intr
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A small 400 by 400 foot body of Nor
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N12°E, 62°NW (about 6,000 ft sout
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The age of the quartz latite porphy
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Tma Mount Aetna quartz monzonite po
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of the Maysville quadrangle and the
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Mount Aetna ring dikes (Tma), one i
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the margins of the pluton, includin
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Shannon (1988). The average of seve
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indicating a granite b composition
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analysis by Crawford (1913), two an
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locally tanish to pinkish gray. It
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quadrangle (tables 1 and 3) were fr
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slices of Paleozoic sedimentary roc
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south-southwest of Maysville is a 9
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There is one additional Paleozoic s
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near the southwest margin of the qu
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eastern contact of the diorite intr
Page 119 and 120: endoskarn zones. The two widely sep
Page 121 and 122: Xhig) along the southeastern contac
Page 123 and 124: Xgd Granodiorite (Early Proterozoic
Page 125 and 126: Hybrid granodiorite is locally deve
Page 127 and 128: Xcs Calc-silicate gneiss (Early Pro
Page 129 and 130: Many of the calc-silicate gneiss zo
Page 131 and 132: typically expressed by intermittent
Page 133 and 134: The field relations and characteris
Page 135 and 136: the north side of all three segment
Page 137 and 138: eplaced by muscovite. The western m
Page 139 and 140: sillimanite-quartz-muscovite that a
Page 141 and 142: sillimanite gneiss (Xmsg) and the m
Page 143 and 144: Figure 35. Outcrop of Proterozoic h
Page 145 and 146: samples) indicates they are compose
Page 147 and 148: Xal Lineated amphibolite (Early Pro
Page 149 and 150: of the Proterozoic metamorphic rock
Page 151 and 152: that the present structural configu
Page 153 and 154: elated to rotation of domain blocks
Page 155 and 156: sometimes terminate at a cross stru
Page 157 and 158: limestone that is exposed in a wind
Page 159 and 160: quadrangle are intimately associate
Page 161 and 162: of the quadrangle. The north-northw
Page 163 and 164: quartz monzonite ring dikes (Tma).
Page 165 and 166: that truncates the Upper Arkansas g
Page 167 and 168: as at the mouth of Squaw Creek. How
Page 169: adjacent to the southwestern edge o
Page 173 and 174: GEOLOGIC HAZARDS Potential geologic
Page 175 and 176: In addition, older landslides may h
Page 177 and 178: sparse vegetation. One such area is
Page 179 and 180: Table 7. Historical (pre-instrument
Page 181 and 182: 4262272N. ECONOMIC GEOLOGY Currentl
Page 183 and 184: A number of the larger pegmatite bo
Page 185 and 186: River placers near Buena Vista (Van
Page 187 and 188: The small mines and prospects along
Page 189 and 190: elatively recent (post-1970) explor
Page 191 and 192: contact of two Quaternary gravels (
Page 193 and 194: quadrangle. The first area is a clu
Page 195 and 196: y Sharp (1976) to be a fault slice
Page 197 and 198: quadrant of the Maysville quadrangl
Page 199 and 200: the large Paleozoic rock outlier) i
Page 201 and 202: WATER RESOURCES Water resources on
Page 203 and 204: water near Maysville is being produ
Page 205 and 206: to Rudy C. Epis: Colorado School of
Page 207 and 208: University, M.Sc. thesis, 50 p. Din
Page 209 and 210: Hutchinson, R.M., and Hedge, C.E.,
Page 211 and 212: Litsey, L.R., 1958, Stratigraphy an
Page 213 and 214: County, Colorado, in Berg, R.R., an
Page 215 and 216: Stark, J.T., and Barnes, F.F., 1935
Page 217 and 218: Tweto, O., 1987, Rock units of the
Page 219 and 220: quadrangle, Colorado: U.S. Geologic
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94A 391996 4263422 Prospect YXp;Xbf
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336A 396189 4274961 Prospect Xgdf B
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854 391849 4268852 42 Adit; Geochem
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Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

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