Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

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Figure 38. Steep rift-related fault cutting California leucogranite (Tcm) in upper Squaw Creek. The fault trends N22 E 79 NW and is subsidiary to major N-NW trending fault related to Collegiate Peaks horst. Fault contains brecciated leucogranite and silicified material. 162
quartz monzonite ring dikes (Tma). The fault crosses Browns Creek and continues northeastward where it intersects the range-front Sawatch fault zone at Raspberry Gulch. On the north side of Browns Creek, geological relations between the Mount Antero leucogranite and the California leucogranite intrusions indicate that the McCoy Creek fault has significant down-to-the-northwest sense of offset (Shannon, 1986 and 1988). The northeast-trending fault extends to the southwest along McCoy Creek into the Garfield quadrangle. In the area of the North Fork, the fault has significant down-to-the northwest offset indicated by the offset of the North Fork leucogranite intrusion (Shannon, 1988). The second major northeast-trending fault in the northwest part of the quadrangle is the range-front Shavano fault zone (figs. 4 and 5). This fault zone has an overall trend of N35°E and defines the main break in slope at the range front. The strong structural and spatial relationship between the northeast-trending faults and the set of northeast-trending rhyolite dikes suggest these fractures were controlling the emplacement of the Oligocene dikes. The group of rhyolite dikes (Trp and Tr) that occur in the Proterozoic rocks have an overall orientation of N25°E with 50°NW dip. Two of the dikes were intruded along the Shavano fault zone and local brecciation indicates continued movement of the fault zone after they were emplaced. The relations described here indicate the presence of a major northeast-trending horst block, herein informally referred to as the Jones Peak horst, which makes up the exposed bedrock area in the northwest part of the Maysville quadrangle (fig. 5). The Jones Peak horst block is about 48,000 ft long and about 13,000 ft wide. It appears to be terminated on the northeast at the north-northwest-trending range-front Sawatch fault zone. The Jones Peak horst extends southwest into the Garfield quadrangle where the continuation of the McCoy Creek fault south of the North fork is uncertain. Estimated offset on the northeast margin of the Jones Peak horst is a minimum of about 600 ft in the North Fork in the Garfield quadrangle, and possibly up to 2,300 ft on Mount White in the Mount Antero quadrangle. No datum allows the determination of offset on the southeast margin of the Jones Peak horst, but a minimum of 4,000 ft of offset on the basement rocks is suggested by the elevation difference from the top of Mount Shavano to the Tertiary and Quaternary sedimentary rocks southeast of the Shavano fault zone. The 163
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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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Page 113 and 114: There is one additional Paleozoic s
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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: of the quadrangle. The north-northw
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Page 169 and 170: adjacent to the southwestern edge o
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
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County, Colorado, in Berg, R.R., an
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Stark, J.T., and Barnes, F.F., 1935
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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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