Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

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southwestern continuation of the Shavano fault is also uncertain. It has been traced to a cluster of mines on the east side of Cree Creek where it is concealed by Quaternary till. The west margin of the Collegiate Peaks horst and the northeast margin of the Jones Peak horst intersect about 4,000 feet north of Mount Shavano in the southwest corner of the Mount Antero quadrangle (figs. 4 and 5). This area is extremely structurally complex and the relative ages of uplift of the two horst blocks is not clear cut. However, the overall pattern of faulting and the cross-cutting relationships with the Oligocene leucogranite intrusions suggests that the northeast-trending Jones Peak horst is probably slightly younger than the north-northwest-trending Collegiate Peaks horst. A west-northwest-trending, mostly inferred fault, herein informally referred to as the Squaw Creek fault extends along Squaw Creek in the northwest quadrant of the Maysville quadrangle (fig. 5). At the very north edge of the quadrangle a zone of small faults on the south side of Squaw Creek cuts the Mount Pomeroy subunit (Tmpp) and controls numerous associated springs. This fault does not appear to cut the northnorthwest-trending fault contact between the Mount Pomeroy subunit (Tmpp) and the California leucogranite (Tcm) at the head of Squaw Creek (in the Mount Antero quadrangle), suggesting that it is older than the north-northwest-trending faults. The west-northwest-trending fault is mostly inferred because it is concealed by glacial gravels (Qpt) in Squaw Creek. However, it may explain apparent offsets (right lateral) in the Mount Princeton (Tmpp)-Proterozoic granodiorite (Xgdf) contact and the Proterozoic granodiorite (Xgdf)-Proterozoic amphibolite gneiss (Xag) contact across Squaw Creek. East of the range front the inferred Squaw Creek fault is associated with a lineament shown on satellite and DEM images that follows the approximate trend of Squaw Creek and is interpreted to be concealed by Quaternary gravels. However, Denesha (2003) found evidence for a west-northwest-trending, north (48° to 82°)-dipping fault cutting the Dry Union Formation on the eastward strike projection of the Squaw Creek fault in the Salida West quadrangle. In addition, an apparent lithologic discontinuity in the character of the Dry Union Formation across this inferred structure is suggested by a distinct change in the assemblage of clast/boulder lithologies. The inferred Squaw Creek fault is parallel to the Salida-Maysville fault; both faults show up as lineaments on DEM images. The Salida-Maysville fault is a major west-northwest-trending transverse fault 164
that truncates the Upper Arkansas graben and separates it from the South Arkansas graben (fig. 5). To the east, it is part of a zone of faults that truncates the northern part of the Sangre de Cristo Range and separates it from the Salida graben (Perry, 1971; Scott and others, 1975; Knepper, 1976). In the Maysville quadrangle, the fault defines a major lithologic discontinuity--on the east, between the two different sequences of the Dry Union Formation (Td on the north and Td2 on the south); on the west, between the Proterozoic terrane (on the south) and the thick sequence of Quaternary gravels and Tertiary Dry Union Formation (Td on the north). The Salida-Maysville fault is mostly inferred where it is concealed by gravels along the South Arkansas River. About 7,000 feet west-northwest of Maysville the location of the fault is more certain and is related to outcrops of faulted, brecciated, and altered Proterozoic granodiorite (Xgd) and intermediate gneiss (Xhig) and a small window of Dry Union Formation exposed in a short unnamed gulch on the north side of the highway. South of the Dry Union Formation exposures, a cut across the Proterozoic rocks exposed a fault with N83°E strike and 63°NW dip, suggesting an orientation or sub-orientation for the Salida-Maysville fault in this area. To the west, the Salida-Maysville fault position is inferred to run on the north side of Cree Creek. Once the Salida-Maysville fault reaches the projected intersection area with the Shavano fault zone at the western boundary of the quadrangle, the evidence for the fault is less certain. Evidence is not compelling to continue the major lithologic discontinuity along the projection of this fault westward into the Garfield quadrangle. If it continued west-northwest, the Salida-Maysville fault would be concealed by Pinedale till (Qpt) in upper Cree Creek and eventually transect the southern part of the Mount Aetna cauldron. Although there are suggestions of a continued west-northwest lineament on satellite and DEM images, there is no evidence for an associated lithologic discontinuity across the Mount Aetna cauldron (Shannon, 1988). In the area of projected intersection of the Shavano fault and the Salida-Maysville fault previous workers (Scott and others, 1975; Tweto and others, 1976) have mapped an irregular north-south fault that truncates the Shavano fault and would also truncate the strike projection of the Salida-Maysville fault. Some evidence for this fault was found in this study, indicated by a broad BR zone extending to the ridge crest on the north side of 165
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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
Page 41 and 42:
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
Page 61 and 62:
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
Page 113 and 114: There is one additional Paleozoic s
Page 115 and 116: 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: quartz monzonite ring dikes (Tma).
Page 167 and 168: as at the mouth of Squaw Creek. How
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
Page 213 and 214: 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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