Ute Pass fault zone (Class A) No. 2327
Last Review Date: 1997-11-06
Compiled in cooperation with the Colorado Geological Survey
citation for this record: Widmann, B.L., compiler, 1997, Fault number 2327, Ute Pass fault zone, in Quaternary fault and fold database of the United States: U.S. Geological Survey website, https://earthquakes.usgs.gov/hazards/qfaults, accessed 04/26/2024 05:42 PM.
| Synopsis |
The Ute Pass fault zone defines the west and southwest margins of the Rampart Range west of Colorado Springs. Tonal and vegetation lineaments and bedrock scarps are discontinuous along the southern trace of the fault, but are lacking along the northern trace. Late Cenozoic movement on the fault is strongly supported along most of the fault (e.g., Taylor, 1975 #2757; Scott and others, 1978 #2735; Kirkham and Rogers, 1981 #792; Dickson, 1986 #2685). However, Quaternary deposits do not appear to be offset across the north end of the fault (Bryant and others, 1981 #2645; Dickson and others, 1986 #2685). Scarps developed on Quaternary (Yarmouth to Illinoian age) rockfall deposits are cited as evidence for Quaternary fault activity on the southern part of the fault by Scott and Wobus (1973 #2738) and Kirkham and Rogers (1981 #792). Unruh and others (1994 #2778) did not recognize any evidence to support mid-Pleistocene to Holocene displacement. However, they did not address the scarps on rockfall deposits as previously presented by Scott and Wobus (1973 #2738) and Kirkham and Rogers (1981 #792). The most recent paleoevent on this fault is herein considered to have occurred during the middle to late Quaternary. |
| Name comments |
The Ute Pass fault zone is defined by a series of five generally northwest-trending faults west of Colorado Springs. The main fault is parallel to the southwest flank of the Rampart Range and Fountain Creek. The faults begin east of Deckers near Devil's Head in the Rampart Range and terminate in a series of splay faults at the southern end of the east flank of the Front Range near Gray Back Peak. Fault ID: Fault 144 in Kirkham and Rogers (1981 #792), fault 142 in Witkind (1976 #2792), and fault number Q77 of Widman and others (1998 #3441). |
| County(s) and State(s) |
TELLER COUNTY, COLORADO EL PASO COUNTY, COLORADO DOUGLAS COUNTY, COLORADO |
| Physiographic province(s) |
SOUTHERN ROCKY MOUNTAINS |
| Reliability of location |
Good Compiled at 1:250,000 scale. Comments: Faults in this zone were mapped by Wobus and Scott (1977 #2794) at a scale of 1:24,000, by Scott and Wobus (1973 #2738) at a scale of 1:62,500, and by Scott and others (1978 #2735) and Bryant and others (1981 #2645) at a scale of 1:250,000. The trace used herein is from Scott and others (1978 #2735) and Bryant and others (1981 #2645).
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| Geologic setting |
The Ute Pass fault zone extends along the western margin of the Rampart Range from near Devils Head to Gray Back Peak and bounds the east side of the Pikes Peak massif west of Colorado Springs. Throw on the fault varies along its length. At the north end the fault plane is nearly vertical. The middle part of the fault near Woodland Park is defined by steeply dipping fault planes that form grabens. The south end of the fault is characterized by west-dipping reverse faults that dip as little as 30? (Epis and others, 1976 #2689). Throw can be generalized as down to west in the north, and down to the east in the south.
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| Length (km) | 71 km. |
| Average strike | N29°W |
| Sense of movement |
Normal, Reverse
Comments: Witkind (1976 #2792) and Bryant and others (1981 #2645) showed the fault zone as high-angle normal. Harms (1959 #2696) and Epis and others (1976 #2689) mapped the middle section of the fault as moderate-angle reverse.
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| Dip |
20° -50° NE, SW
Comments: The fault dips southwest at the north end and northeast at the south end (Epis and others, 1976 #2689). Dip angles are considered to be between 20? -50? (Harms, 1959 #2696; Epis and others, 1976 #2689).
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| Paleoseismology studies |
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| Geomorphic expression |
The fault zone is marked by subtle, discontinuous, anomalous lineaments (visible on aerial photos) that extend through rockfall deposits at the south end of the fault (Kirkham and Rogers, 1981 #792). A prominent scarp is onVerdos Alluvium at the south end of the fault (Scott and Wobus, 1973 #2738). Unruh and others (1994 #2778) reported discontinuous tonal and vegetation lineaments, as well as an east-facing bedrock scarp and a southwest-facing scarp along the south end of the fault.
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| Age of faulted surficial deposits | The fault is primarily in Precambrian bedrock. Scott and Wobus (1973 #2738) and Wobus and Scott (1977 #2794) mapped the fault as concealed by Quaternary deposits. Later, Scott and others (1978 #2735) mapped offset Pliocene and Miocene gravel deposits. Pleistocene fan alluvium abuts the fault according to Bryant and others (1981 #2645). The best evidence for Quaternary fault activity is limited to the south end of the fault zone near Cheyenne Mountain, where development of a prominent scarp on Verdos Alluvium and scarps extending across Pleistocene rockfall deposits indicated youthful fault activity to Kirkham and Rogers (1981 #792). Unruh and others (1994 #2778), however, found no evidence of offset in late Pleistocene to Holocene deposits along the south end of the fault. Pleistocene to Holocene deposits are not disturbed across the north end of the fault (Dickson and others, 1986 #2685; Geotechnical Advisory Committee, 1986 #2691). |
| Historic earthquake | |
| Most recent prehistoric deformation |
middle and late Quaternary (<750 ka)
Comments: Neogene fault activity is apparent based on offset of Pliocene and Miocene gravels (Scott and Wobus, 1973 #2738), and 300 m of throw on the fault since the Eocene was recorded by Epis and Chapin (1975 #2689). Evidence for Quaternary movement is not observed north of Woodland Park (Dickson and others, 1986 #2685). Although evidence for Quaternary movement on the fault is not definitive, geomorphic features on the south end of the fault near Cheyenne Mountain suggest the possiblity of two ruptures during the Quaternary. Scarps on and lineations in rockfall deposits are believed to represent the second of the two ruptures, whereas the rockfalls themselves are interpretted as resulting from an earthquake during the Yarmouth interglacial period (Scott and Wobus, 1973 #2738). Howard and others (1978 #312) showed this as a fault with late Quaternary movement. Kirkham and Rogers (1981 #792) stated that the Slocum Alluvium is not offset across the fault, thus constraining the timing of the second period of activity to between the Yarmouth interglacial period and the Illinoian glacial period. Unruh and others (1994 #2778) found no evidence of offset in late Pleistocene to Holocene deposits along the south end of the fault and concluded that scarp features are fault-line scarps or the result of diferential erosion. Evidence against Quaternary movement provided by Unruh and others (1994 #2778) does not address all of the arguments for Quaternary movement presented by Scott and Wobus (1973 #2738), Kirkham and Rogers (1981 #792), and Dickson and others (1986 #2685) and is considered insufficient to warrant discounting the fault zone as a middle to late Quaternary structure.
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| Recurrence interval | |
| Slip-rate category |
Less than 0.2 mm/yr
Comments: Despite the possibility of two events during the Yarmouth to Illinoian, a long-term slip rate of <0.2 mm/yr wasestimated for this fault by Widmann and others (1998 #3441) based on the small size of the scarps and the fact that the fault apparently has not ruptured since the initial deposition of the Slocum Alluvium (about 130 ka). Jack Benjamin and Associates and Geomatrix Consultants (1996 #2691) calculated a long-term average slip rate of 0.01 mm/yr for the Ute Pass fault zone. |
| Date and Compiler(s) |
1997
Beth L. Widmann, Colorado Geological Survey |
| References |
#2645 Bryant, B., McGrew, L.W., and Wobus, R.A., 1981, Geologic map of the Denver 1° x 2° quadrangle, north-central Colorado: U.S. Geological Survey Miscellaneous Geologic Investigations I-1163. #2685 Dickson, P.A., Kewer, R.P., and Wright, J.E., 1986, Regional fault study—Central Front Range, Colorado, in Rogers, W.P., and Kirkham, R.M., eds., Contributions to Colorado tectonics and seismicity—A 1986 update: Colorado Geologic Survey Special Publication 28, p. 172-185. #2689 Epis, R.C., Scott, G.R., Taylor, R.B., and Chapin, C.E., 1976, Cenozoic volcanic, tectonic, and geomorphic features of central Colorado: Colorado School of Mines Professional Contributions no. 8, 323-338 p. #2691 Geotechnical Advisory Committee, 1986, Geologic and seismotectonic investigations, east-central Front Range, Colorado: Denver Water Department, Summary Report, 89 p. #2696 Harms, J.C., 1959, Structural geology of the eastern flank of the southern Front Range, Colorado: Boulder, Colorado, University of Colorado, unpublished Ph.D. dissertation, 165 p. #312 Howard, K.A., Aaron, J.M., Brabb, E.E., Brock, M.R., Gower, H.D., Hunt, S.J., Milton, D.J., Muehlberger, W.R., Nakata, J.K., Plafker, G., Prowell, D.C., Wallace, R.E., and Witkind, I.J., 1978, Preliminary map of young faults in the United States as a guide to possible fault activity: U.S. Geological Survey Miscellaneous Field Studies Map MF-916, 2 sheets, scale 1:5,000,000. #2703 Jack Benjamin & Associates and Geomatrix Consultants, 1996, Probabilistic seismic hazard assessment for the U.S. Army chemical disposal facility, Pueblo Depot Activity, Colorado: Technical report to Science Applications International Corporation, Maryland, under Contract JBA 148-130-PU-002. #792 Kirkham, R.M., and Rogers, W.P., 1981, Earthquake potential in Colorado: Colorado Geological Survey Bulletin 43, 171 p., 3 pls. #2738 Scott, G.R., and Wobus, R.A., 1973, Reconnaissance geologic map of Colorado Springs and vicinity, Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF-482. #2735 Scott, G.R., Taylor, R.B., Epis, R.C., and Wobus, R.A., 1978, Geologic map of the Pueblo 1° x 2° quadrangle, south-central Colorado: U.S. Geological Survey Miscellaneous Geologic Investigations I-1022. #2757 Taylor, R.B., 1975, Neogene tectonism in south-central Colorado, in Curtis, B.F., ed., Cenozoic history of the southern Rocky Mountains: Geological Society of America Memoir 144, p. 211-226. #2776 Unruh, J.R., Sawyer, T.L., and Lettis, W.R., 1992, Seismotectonic evaluation of Green Mountain Dam, Shadow Mountain Dam, Grandby Dam, and Willow Creek Dam, Colorado-Big Thompson Project: Technical report to U.S. Bureau of Reclamation, Denver, Colorado, 78 p. #2778 Unruh, J.R., Wong, I.G., Hitchcock, C.S., Bott, J.D.J., Silva, W.J., and Lettis, W.R., 1994, Seismotectonic evaluation, Pueblo Dam, Fryingpan-Arkansas Project, south-central Colorado: U.S. Bureau of Reclamation, 134 p. #3441 Widmann, B.L., Kirkham, R.M., and Rogers, W.P., 1998, Preliminary Quaternary fault and fold map and database of Colorado: Colorado Geological Survey Open-File Report 98-8, 331 p., 1 pl., scale 1:500,000. #2792 Witkind, I.J., 1976, Preliminary map showing known and suspected active faults in Colorado: U.S. Geological Survey Open-File Report 76-154. #2794 Wobus, R.A., and Scott, G.R., 1977, Reconnaissance geologic map of the Cascade quadrangle, El Paso County, Colorado: U.S. Geological Survey Open-File Report 77-138. |