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Figure 1. Map of Colorado showing Interstate Highway 70 (red line) and areas of detailed geologic mapping (yellow polygons) completed by USGS geologists as part of this project. |
Rapid population growth along the Interstate-70 corridor in western Colorado between the Frisco-Dillon area and the Grand Junction area prompted the USGS and the Colorado Geological Survey to join forces to form cooperative geologic mapping teams. For its part, the USGS produced 14 detailed geologic maps along the corridor as well as many related publications during the project's existence. Geologic hazards and potential mineral resources were identified and characterized by the geological mapping program. The public in Mesa, Garfield, Eagle, and Summit Counties, as well as city, county, state, and federal agencies in those counties, can use these maps to make land-use decisions to either mitigate or avoid geologic hazards, and thus potentially save money, property, and lives.
Large landslides cover many mountainsides throughout western Colorado, and many of these slides are near towns, recreational facilities, railroads, buried utilities, irrigation ditches, and major highways, including the I-70 corridor (Fig. 2). Landslide is a general term that includes a wide variety of ways that masses of rock and earth move down slopes. Many of these landslides are less than 10,000 years old, some of them are still active, and a number of them moved downhill at life-threatening speeds when they became reactivated. Many old inactive landslides could be reactivated by periods of heavy precipitation or by human activities such as making cuts in hillsides for roads or buildings. Excavations for roads or buildings can reactivate landslides, because the lateral support that kept the rocks and earth in place has been reduced or removed. New landslides in areas where no slides have been recorded can be initiated by the same types of natural or man-made disturbances. As population growth continues in western Colorado, the chance of landslides affecting people increases.
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Figure 2. This aerial photograph shows a relatively old debris flow and a younger landslide. The town of Palisade is on the north side of the Colorado River. The debris flow is over three miles long. Two streams have cut deep, narrow valleys into the debris flow. The landslide, recognized by its broken and hummocky surface, is just southwest of the debris flow. The landslide occurred when a 2.2-mile-long section of the Horse Mountain pediment and underlying Mancos Shale moved down slope. |
In the Grand Mesa area, landslide deposits are numerous, particularly along the steep slopes surrounding much of the mesa, and some of these landslides are several square miles in extent. Several types of landslides occur in this area; these include earth flows, earth slumps, debris flows, rock slumps, rock-block slides, and combination of these types. Rock slumps and rock-block slides along the margins of Grand Mesa are commonly caused by sliding on the weak claystone layer underlying the resistant basalt cap on the mesa. Earth flows are also common along the flanks of Grand Mesa, which are underlain by the multicolored shale and sandstone of the Wasatch Formation. These earth flows may be as much as one mile long, a tenth of a mile wide, and have lobe-shaped ends. Based on studies of how deeply erosion has cut into these flows, it is estimated that these earth flows range in age from tens of thousands of years to presently active. Some large debris flows, which are similar to earth flows except that they contain more water and hence can move quite rapidly, originated along the western flank of Grand Mesa and flowed several miles to the Colorado River. In fact, geologic evidence indicates that the Colorado River near the town of Rifle was once dammed by a debris flow. Under the right conditions, debris flows can race down slopes as fast as 100 miles per hour with potentially disastrous results.
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Figure 3. View of debris flow, I-70, and the Colorado River, looking east (upstream) toward Glenwood Springs. The flow exited the canyon in the steep slopes of Storm King Mountain on the left, filled a portion of the west-bound lanes, overtopped the concrete dividers, crossed the east-bound lanes, and formed the small fan-shaped deposit that partially dammed the river. (Photograph by Jim Scheidt, Bureau of Land Management, Colorado). |
Citizens of Glenwood Springs and travelers on I-70 experienced the problems when precipitation triggered a number of debris flows on Storm King Mountain, closing I-70 once in the summer of 1994 and twice again in 1995 (Fig. 3). The story of these debris flows began with the South Canyon Fire on Storm King Mountain northwest of Glenwood Springs in July 1994. The fire burned 2,000 acres of piñon-juniper and gamble oak forest and killed 14 fire fighters. On the night of September 1, 1994, torrential rains dumped water on slopes denuded by the fire. The resulting flash flood picked up mud, sand, rocks, and burned trees and formed debris flows that came crashing down normally dry washes onto I-70 in four places. Thirty cars traveling on the highway at the time were engulfed by the debris flows, but luckily only minor injuries were reported. At one location, material overtopped the concrete dividers between the east- and west-bound lanes of the interstate and flowed into the Colorado River where the debris blocked nearly half the river channel.
In response to this event, studies were undertaken by personnel from the Geologic Hazards Team of the USGS and the Colorado Geological Survey. Detailed mapping from aerial photographs taken on November 10, 1994, coupled with extensive field observations and measurements show that the net result of the September 1994 rainstorm was to flush loose burned soil and ash as well as sediment from the side channels, transport coarser debris from the main channels, and erode approximately 15% of the burned soil from the hillsides to an average depth of 1.5 inches. This material was incorporated into the debris flows that inundated I-70 and flowed into the Colorado River. The flows covered approximately 35 acres along I-70 with roughly 91,000 cubic yards of material. The debris flows moved at rates calculated to have been from 10 to 28 feet per second (7 to 19 miles per hour) and discharged between 40 and 150 cubic yards of debris per second.
Although the burned area was seeded in November of 1994, the potential remains for more destructive debris-flows and high-volume surface-water floods. The lack of vegetation on the slopes reduced the ability of the ground surface to retard rainfall runoff and increased the chance of high-volume floods. These floods may result in future debris flows if considerable downcutting occurs along stream channels. This process occurred in the spring of 1995 when 0.5 inches of precipitation fell in 30 minutes at the head of the easternmost drainage in the watershed; as much as 10 feet of downcutting occurred along the main channel and debris-flows were observed following the rainstorm.
The results of these studies and the status of the other hazards on Storm King Mountain were conveyed to the Garfield County Commissioners, Colorado State Highway Patrol, and Colorado Department of Transportation for their use in planning emergency response.
Other types of geological hazards are present in the Carbondale, Glenwood Springs, Gypsum, and Eagle areas, which are locally underlain by soluble evaporite deposits (salt and gypsum). These deposits have affected these areas in several ways, including formation of sinkholes by solution of underground deposits, tilting of river terraces, disruption of stream drainage, contamination of ground and surface water, and displacement of basalt flows. In some cases, sinkhole formation was initiated by irrigation. One sinkhole formed under an irrigation ditch, created a 6-foot by 8-foot hole about 50 feet deep. The sinkhole diverted irrigation water downhill to a county road that was deeply eroded by the water. Dissolved salts contaminate groundwater, and salts dissolved in water issuing from hot springs greatly increase the salinity of the Colorado River downstream of the springs. Concrete foundations built on geologic materials containing gypsum and salt in the bedrock become corroded and weakened. Although the effects of sinkhole formation and slow subsidence are commonly not as dramatic as the effects of debris flow or a landslide, the financial losses related to damaged foundations and roadways, collapse of agricultural lands, contaminated waters, and damaged underground utilities can be substantial. Coordinated detailed geologic mapping by geologists of the Colorado Geological Survey and the USGS Geologic Mapping Team examined these areas threatened by potential solution of evaporites.
Soil stability problems also occur along the I-70 corridor. For example, another significant geologic hazard involves hydrocompaction of rapidly deposited, low-density sediments, such as wind-deposited sandy silt referred to as loess (Fig. 4). Saturation of low-density sediments by human activity such as irrigation, lawn watering, road construction, and artificial ponding was responsible for most examples of hydrocompaction. Cavities formed during hydrocompaction can cause loss of support and possible collapse of foundations or pavement. Another example of soil instability is related to a process called piping where water erodes pipe-shaped voids that may be concealed by the surface soil. Piping occurs locally in fine-grained deposits such as loess and also in gypsum-bearing soils. Deposits of loess commonly mantle river terraces and mesas that are used for agriculture and housing developments. Structural damage related to piping may be similar to that caused by hydrocompaction. Locally hydrocompaction and piping may operate together to cause collapse. Geologic mapping by both of the geological surveys identified areas where these processes are likely to occur.
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Figure 4. A sinkhole near the town of Carbondale that was initiated by hydrocompaction of surficial deposits and was enlarged by piping into a void caused by solution of the underlying Eagle Valley Evaporite. The collapse feature is about 80 feet across and about 10 feet deep. (Courtesy of Colorado Geological Survey). |
Expansive as well as collapsing soils and surficial deposits also cause extensive damage to foundations and pavement (Fig. 5). Areas underlain by the upper part of the Mancos Shale in Grand Valley of Mesa and Montrose Counties are locally susceptible to problems caused by materials that expand when wet and contract when dry.
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Figure 5. Settling and cracking of the walls at the corner of a church in Olathe, Montrose County. The heavier corner of this structure settled more than the adjacent sides (photo by Wallace R. Hansen, U.S. Geological Survey). |
Detailed geologic maps of hazard-prone areas such as those along the I-70 corridor provide our society with some information needed to make intelligent land use decisions that can save money and possibly lives in the future.
Geologic Maps
Bryant, Bruce, Shroba, R.R., Harding, A.E., and Murray, K.E., 2002, Geologic map of the Storm King Mountain quadrangle, Garfield County, Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF-2389, scale 1:24,000.
Carrara, P.E., 2000, Geologic map of the Palisade Quadrangle, Mesa County, Colorado: U.S. Geological Survey Miscellaneous Field Investigations Map MF-2326, scale 1:24,000.
Carrara, P.E., 2001, Geologic map of the Clifton Quadrangle, Mesa County, Colorado: U.S. Geological Survey Miscellaneous Field Investigations Map MF-2359, scale 1:24,000.
Kellogg, K.S., 2002, Geologic map of the Dillon quadrangle, Summit and Grand Counties, Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF-2390, scale 1:24,000.
Kellogg, K.S., Bartos, P.J., and Williams, C.L., 2002, Geologic map of the Frisco Quadrangle, Summit County, Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF-2340, scale 1:24,000.
Kellogg, K.S., Bryant, Bruce, and Redsteer, M.H., 2003, Geologic map of the Vail East quadrangle, Eagle County, Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF-2375, scale 1:24,000.
Lidke, D.J., 1998, Geologic map of the Wolcott quadrangle, Eagle County, Colorado: U.S. Geological Survey Geologic Investigations Series Map I-2656, scale 1:24,000.
Lidke, D.J., 2002, Geologic map of the Eagle quadrangle, Eagle County, Colorado: U.S. Geological Survey, Miscellaneous Field Studies Map MF-2361, scale 1:24,000.
Perry, W.J., Shroba, R.R., Scott, R.B., and Maldonado, Florian, 2003, Geologic map of the Horse Mountain Quadrangle, Garfield County, Colorado: U.S. Geological Survey, Miscellaneous Field Studies Map MF-2415, scale 1:24000.
Scott, R.B., Carrara, P.E., Hood, W.C., and Murray, K.E., 2002, Geologic map of the Grand Junction Quadrangle, Mesa County, Colorado: U.S. Geological Survey Miscellaneous Field Investigations Map MF-2363, scale 1:24,000.
Scott, R.B., Harding, A.E., Hood, W.C., Cole, R.D., Livaccari, R.F., Johnson, J.B., Shroba, R.R., and Dickerson, R.P., 2001, Geologic map of Colorado National Monument and adjacent areas, Mesa County, Colorado: U.S. Geological Survey Geologic Investigations Series Map I-2740, scale 1:24,000.
Scott, R.B., Lidke, D.J. and Grunwald, D.J., 2002, Geologic map of the Vail West quadrangle, Eagle County, Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF-2369, scale 1:24,000.
Scott, R.B., Shroba, R. R., and Egger, A.E., 2001, Geologic map of the Rifle Falls quadrangle, Garfield County, Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF-2341, scale 1:24,000.
Shroba, R.R., and Scott, R.B., 2001, Geologic map of the Silt quadrangle, Garfield County, Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF-2331, scale 1:24,000.
Bryant, Bruce, Shroba, R.R., and Harding, A.E., 1998, Revised preliminary geologic map of the Storm King Mountain quadrangle, Garfield County, Colorado: U.S. Geological Survey Open-File Report 98-472, 36 p., scale 1:24,000.
Budahn, J.R., Unruh, D.M., Kunk, M.J., Byers, F.M., Jr., Kirkham, R.M., and Streufert, R.K., 2002, Correlation of late Cenozoic basaltic lava flows in the Carbondale and Eagle collapse centers in west-central Colorado based on geochemical isotopic, age, and petrologic data, in Kirkham, R.M., Scott, R.B., and Judkins, T.W., eds., Late Cenozoic evaporite tectonism and volcanism in west-central Colorado: Geological Society of America Special Paper 366, p. 167-196.
Carrara, P.E., 1997, Preliminary geologic map of the Palisade Quadrangle, Mesa County, Colorado: U.S. Geological Survey Open-File Report 97- 462, scale 1:24,000.
Hudson, M.R., Harlan, S.S., and Kirkham, R.M., 2002, Paleomagnetic investigation of the structural deformation and magnetstratigraphy of Neogene basaltic flows in western Colorado, in Kirkham, R.M., Scott, R.B., and Judkins, T.W., eds., Late Cenozoic evaporite tectonism and volcanism in west-central Colorado: Geological Society of America Special Paper 366, p. 197-212.
Kellogg, K.S., 1997, Geologic map of the Dillon quadrangle, Summit and Grand Counties, Colorado: U.S. Geological Survey Open-File Report 97-738, scale 1:24,000.
Kellogg, K.S., 1999, Neogene basins of the northern Rio Grande Rift--partitioning and asymmetry inherited from Laramide and older uplifts: Tectonophysics, v. 305, p. 141-152.
Kellogg, K.S., 2001, Tectonic controls on a large landslide complex-Williams Fork Mountains near Dillon, Colorado: Geomorphology, v. 41, p. 355-368.
Kirkham, R.M., Bryant, Bruce, Streufert, R.K., and Shroba, R.R., 1996, Field trip guidebook on the geology and geologic hazards of the Glenwood Springs area, Colorado, in Thompson, R.A., Hudson, M.R., and Pillmore, C.L., eds., Geologic Excursions to the Rocky Mountains and beyond: Colorado Geological Survey Special Publication 44, CD-ROM, 38 p.
Kirkham, R.M., Kunk, M.J., Bryant, Bruce, and Streufert, R.K., 2001, Constraints on timing and rates of late Cenozoic incision by the Colorado River in Glenwood Canyon, Colorado: a preliminary synopsis, in Young, R.A. and Spamm, E.E., eds., The Colorado River: Origin and evolution: Grand Canyon, Arizona, Grand Canyon Association Monograph 12, p. 113-116.
Kirkham, R.M. and Scott, R.B., 2002, Introduction to late Cenozoic evaporate tectonism and volcanism in west-central Colorado, in Kirkham, R.M., Scott, R.B., and Judkins, T.W., eds., Late Cenozoic evaporite tectonism and volcanism in west-central Colorado: Geological Society of America Special Paper 366, p. 1-14.
Kirkham, R.M., Scott, R.B., and Judkins, T.W., eds., 2002, Late Cenozoic evaporate tectonism and volcanism in west-central Colorado: Geological Society of America, Special Paper 366, 234 p.
Kirkham, R.M., Streufert, R.K., Kunk, M.J., Budahn, J.R., Hudson, M.R, and Perry, W.J., 2002, Evaporite tectonism in the lower Roaring Fork River valley, west-central Colorado, in Kirkham, R.M., Scott, R.B., and Judkins, T.W., eds., Late Cenozoic evaporite tectonism and volcanism in west-central Colorado: Geological Society of America Special Paper 366, p. 73-99.
Kunk, M.J., Budhan, J.R., Unruh, D.M., Stanley, J.O., Kirkham, R.M., Bryant, Bruce, Scott, R.B., Lidke, D.J., and Streufert, R.K., 2002,40Ar/39Ar ages of Late Cenozoic volcanic rocks within and around the Carbondale and Eagle collapse center, Colorado: Constraints on the timing of evaporite collapse and incision of the Colorado River, in Kirkham, R.M., Scott, R.B., and Judkins, T.W., eds., Late Cenozoic evaporite tectonism and volcanism in west-central Colorado: Geological Society of America Special Paper 366, p. 213-234.
Lidke, D.J., Hudson, M.R, Scott, R.B., Kunk, M.J., Shroba, R.R., Perry, W.J., Jr., Budahn, J.R., Kirkham, R.M., and Streufert, R.K., 2002, Eagle collapse center: Overview and evidence for Neogene evaporite-related deformation in the Eagle River basin, Colorado, in Kirkham, R.M., Scott, R.B., and Judkins, T.W., eds., Late Cenozoic evaporite tectonism and volcanism in west-central Colorado: Geological Society of America Special Paper 366, p. 101-120.
Naeser, C.W., Bryant, Bruce, Kunk, M.J., Kellogg, K.S., Donelick, R.A., and Perry, W.J., Jr., 2002, Tertiary cooling and tectonic history of the White River uplift, Gore Range, and western Front Range, central Colorado: Evidence from fission-track and 40Ar/39Ar ages, in Kirkham, R.M., Scott, R.B., and Judkins, T.W., eds., Late Cenozoic evaporite tectonism and volcanism in west-central Colorado: Geological Society of America Special Paper 366, p. 31-54.
Perry, W.J., Jr., Miller, J.J., and Scott, R.B., 2002, Implications for evaporate tectonism in the Carbondale and Eagle collapse centers of west-central Colorado, based on reprocessed seismic reflection data, in Kirkham, R.M., Scott, R.B., and Judkins, T.W., eds., Late Cenozoic evaporite tectonism and volcanism in west-central Colorado: Geological Society of America Special Paper 366, p. 55-72.
Scott, R.B., Bryant, Bruce, and Perry, W.J., 2002, Late Cenozoic deformation by evaporate tectonism in the Grand Hogback monocline, southwest of the White River uplift, Colorado, in Kirkham, R.M., Scott, R.B., and Judkins, T.W., eds., Late Cenozoic evaporite tectonism and volcanism in west-central Colorado: Geological Society of America Special Paper 366, p. 121-147.
Scott, R. B., Lidke, D.J., Hudson, M.R., Perry, W.J., Jr., Bryant, Bruce, Kunk, M.J., Budahn, J.R., and Byers, F.M., Jr., 1999, Active evaporite tectonism and collapse in the Eagle River valley and the southwestern flank of the White River uplift, Colorado, in Lageson, D.R., Lester, A.P., and Trudgill, B.D., eds., Colorado and Adjacent Areas: Boulder, Colorado, Geological Society of America Field Guide 1, p. 97-114.
Scott, R.B., Lidke, D.J., Shroba, R.R., Hudson, M.R., Kunk, M.J., Perry, W.J., Jr., and Bryant, Bruce, 1998, Large-scale active collapse in western Colorado: Interaction of salt tectonism and dissolution, in Van Brahana, J.V., Eskstein, Yoram, Ongley, L.K., Schneider, Robert, and Moore, J.E., eds., Gambling with groundwater-Physical, chemical, and biological aspects of aquifer-stream relations: Proceedings of the joint meeting of the XXVIII Congress of the International Association of Hydrologists and the Annual Meeting of the American Institute of Hydrologists, Las Vegas, Nevada, USA, September 24-October 2, 1998, p. 195-205.
Scott, R.B. and Shroba, R.R., 1997, Revised preliminary geologic map of the New Castle quadrangle, Garfield County, Colorado: U.S. Geological Survey Open-File Report 97-737, 30 p., scale 1:24,000.
Shroba, R.R., Green, M.W., and Fairer, G.M., 1995, Preliminary geologic map of the Rifle quadrangle, Garfield County, Colorado: U.S. Geological Survey Open-File Report 95-52, 22 p., scale 1:24,000.
Shroba, R.R. and Scott, R.B., 1997, Revised preliminary geologic map of the Rifle quadrangle, Garfield County, Colorado: U.S. Geological Survey Open-File Report 97-852, 21 p., scale 1:24,000.
Steven, T.A., 2002, Late Cenozoic tectonic and geomorphic framework surrounding the evaporate dissolution area in west-central Colorado, in Kirkham, R.M., Scott, R.B., and Judkins, T.W., eds., Late Cenozoic evaporite tectonism and volcanism in west-central Colorado: Geological Society of America Special Paper 366, p. 15-30.
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