Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

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earthquake swarm (Kirkham and Rogers, 2000), so the causative fault(s) are unknown. Despite the relative scarcity of historic seismicity, geologic evidence suggests that some faults in the quadrangle have been active in Quaternary time (see previous section on Structural Geology, Quaternary Deformation). For purposes of estimating earthquake hazards, we assume that the Shavano fault will rupture along with the southern Sawatch fault, as the latter is defined by the U.S. Geological Survey. According to the US Geological Survey’s National Seismic Hazard Map (http://earthquake.usgs.gov/research/hazmaps/products_data/2002/faults2002.php), the southern Sawatch fault can generate earthquakes up to (moment) Magnitude 7.0. This magnitude estimate is based primarily on the fault length (28 mi), a length which includes the Shavano fault zone. In the event of an M 7.0 earthquake on the Sawatch fault zone, hazards would be related to strong ground shaking, shaking-induced ground failure such as liquefaction and landslides, and fault surface rupture. For the town of Maysville (zip code 81211), in any 50 year-long period, a 10 percent chance exists that peak horizontal ground shaking will be stronger than 0.06g (1g= gravitational acceleration), a 5 percent chance it will be stronger than 0.9g, and a 2 percent chance it will be stronger than 0.20g (U.S. Geological Survey 2002 National Seismic Harazd Maps). The latter estimate (2 percent chance in 50 years) is statistically equivalent to the largest earthquake expected in about 2,500 years. However, the recurrence interval of surface-rupturing earthquakes on the Sawatch fault zone is much longer than 2,500 years (estimated as 10,000 to 40,000 years farther north in the Buena Vista West quadrangle; see McCalpin and Shannon, 2005), so the actual shaking that might occur during a surface-rupturing earthquake will be greater than 0.20g at Maysville and much greater closer to the Sawatch fault zone. More precise estimates for any specific site would require a site-specific ground-motion study. The strong shaking may induce landslides and rockfalls in the Sawatch Range and liquefaction of areas containing high water tables (less than 30 ft deep) where the aquifer is mainly sand. The latter condition may exist in parts of the broad flood plain of the South Arkansas River (map unit Qal) downstream from Maysville, where water levels in wells stand only 4-20 ft below the surface. 178
Table 7. Historical (pre-instrumental) earthquakes in or near the Maysville quadrangle, according to Kirkham and Rogers (2000). All these events occurred a few miles west of the Maysville 7.5’ quadrangle, in the adjacent Garfield 7.5’ quadrangle. ID DATE ORIGIN TIME EPICENTRAL UTM UTM INTENSITY REFERENCES YEAR MONTH DAY (UTC) LOCATION (E) (N) (MM) 34 1921 FEB. 6 06:15 ST. ELMO 386794 4272984 IV 52,112 35 1921 FEB. 6 06:25 GARFIELD 386794 4272984 IV 52,112 36 1921 FEB. 6 06:30 ST. ELMO 386794 4272984 IV 52,112 37 1921 FEB. 17 01:45 GARFIELD 386794 4272984 III 52 38 1921 FEB. 17 13:05 GARFIELD 386794 4272984 III 52 39 1921 FEB. 26 15:55 GARFIELD 386794 4272984 III 52 40 1921 FEB. 7 17:00 GARFIELD 386794 4272984 III 52 41 1921 MAR. 4 06:00 GARFIELD 386794 4272984 II 52 42 1921 MAR. 8 19:15 GARFIELD 386794 4272984 IV 52 43 1921 MAR. 9 01:25 GARFIELD 386794 4272984 III 52 44 1921 MAR. 12 07:00 GARFIELD 386794 4272984 II 52 45 1921 MAR. 22 21:45 GARFIELD 386794 4272984 III 52 46 1921 JUL. 27 21:30 GARFIELD 386794 4272984 III 52,112 47 1921 JUL. 29 02:55 GARFIELD 386794 4272984 III 52,112 References: 52= Humphreys, 1914-1924; 112= Stover and others, 1984. 179
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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
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endoskarn zones. The two widely sep
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Xhig) along the southeastern contac
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Xgd Granodiorite (Early Proterozoic
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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 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: sparse vegetation. One such area is
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
Page 221 and 222: 94A 391996 4263422 Prospect YXp;Xbf
Page 223 and 224: 336A 396189 4274961 Prospect Xgdf B
Page 225: 854 391849 4268852 42 Adit; Geochem
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Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

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