Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

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gradually bends about 70° to become the Shavano fault zone, which trends N50°E. Thus, this swarm of four faults appears to represent a southward continuation of the Sawatch fault zone, composed of distributed down-to-the-east step faulting. This fault geometry implies that the down-to-the-east Quaternary displacement on the western side of the Upper Arkansas graben is partitioned between components, a larger one at the range front (Shavano fault zone), and a smaller one that trends south-southeast into the valley fill (southward continuation of the Sawatch fault zone). DISCUSSION The tectonic-structural setting of the Maysville quadrangle is complicated by its location along the northern part of the complex transfer or accommodation zone that separates the Upper Arkansas axial basin from the San Luis axial basin (fig. 5). Chapin and Cather (1994) suggested a model that relates northeast-trending accommodation zones that segment the Rio Grande rift to pre-existing transverse structural lineaments related to Late Cenozoic clockwise rotation of the Colorado Plateau. They suggested the poorly exposed and less constrained accommodation zone associated with the Upper Arkansas and San Luis grabens is the northeast-trending Villa Grove accommodation zone. Additional complications are suggested by the developing picture of rift shoulder uplifts, extra- and intra-graben horst blocks, and complex compartmentalization of the main axial grabens (fig. 39). Two previously recognized subparallel horst blocks that impinge on the east side of the Upper Arkansas graben are the Browns Canyon horst and the large Sangre de Cristo horst (Knepper, 1974 and Taylor, 1975). The Browns Canyon horst (informal name used herein) occurs in the southern Mosquito Range on the east edge of the Upper Arkansas graben about 6 mi northnorthwest of Salida. It is about 6 mi long, 1.5 mi wide and trends about N40°W. The main Sangre de Cristo Range trends about N28°W along the western side of the San Luis Valley and bends to about N45°W in the Villa Grove area. The very northern end of the range is oriented about N67°W and is an intragraben horst (or tilted block) where it is 168
adjacent to the southwestern edge of the Salida graben. The Salida-Maysville fault is the structural boundary between the Sangre de Cristo horst and the Salida graben in the east and the structural boundary between the South Arkansas graben and the Upper Arkansas graben in the west. The fault continues westward across the southwestern part of the Maysville quadrangle and defines the structural boundary between the Proterozoic terrane outside the west margin of the South Arkansas graben and the Tertiary Dry Union Formation in the southwestern part of the Upper Arkansas graben. Thus, the Salida- Maysville fault, which trends about N70°W across the quadrangle, is a major westnorthwest-trending transverse structure associated with the Sangre de Cristo horst and defines the southern margin of the Upper Arkansas graben. Two horst blocks have been recognized on the west side of the rift: the N15°- to 35°W-trending Collegiate Peaks horst (Shannon, 1988) and the about N35°E-trending Jones Peak horst informally defined in this report (fig. 39). The southern part of the Collegiate Peaks horst is oriented about N15 W and is about 10 mi long and 12,000 ft wide from Browns Creek to Sheep Mountain. It bends to a N35°W trend in the area southwest of Mount Yale where it is less defined but may be over 15,000 ft wide. The Jones Peak horst trends N35° to 40°E and is about 40,000 ft long and 13,000 ft wide. Evidence also exists that the axial grabens are subdivided and compartmentalized into sub-grabens and/or broken up by smaller intragraben horsts. McCalpin and Shannon (2005) showed preliminary evidence for the presence of a N40°W-trending intragraben graben in the Maxwell Park area in the Buena Vista West quadrangle. The postulated Salida graben in the eastern part of the southern Upper Arkansas graben (Knepper, 1976) may extend west and include the area between the Squaw Creek fault and the Salida- Maysville fault as suggested in this report (fig. 39). If so, the Salida graben trends about N70°W and is about 17 mi long and 4 mi wide. Additional evidence for the westward continuation of the Salida graben is the major change in the composition of the Dry Union conglomerate clasts across the Squaw Creek fault. Detailed studies of Dry Union clast compositions may provide important clues about the location of sub-grabens and the bounding faults. Deep drilling for water wells or exploratory geothermal wells, and the ability to log those wells, would also help delineate these boundaries. 169
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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
Page 117 and 118: 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: as at the mouth of Squaw Creek. How
Page 171 and 172: graben and the Upper Arkansas Valle
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
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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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