Slope Stability of Proposed Ski Facilities 

at the Southeast Side of Snodgrass Mountain, 

Gunnison County, Colorado 

Open-File Report 1996-701


U.S. Department of the Interior 

U.S. Geological Survey 
U.S. DEPARTMENT OF THE INTERIOR 

U.S. GEOLOGICAL SURVEY 

Slope Stability of Proposed Ski Facilities 

at the Southeast Side of Snodgrass Mountain, 

Gunnison County, Colorado

by 

Rex L. Baum1

Open-File Report 96-701 

This report has not been reviewed for conformity with U.S. Geological Survey editorial standards 

and stratigraphic nomenclature. Any use of trade or company names is for descriptive purposes 

only and does not imply endorsement by the U.S. Geological Survey. 

1Denver, Colorado 

1996 
Slope Stability of Proposed Ski Facilities at the Southeast Side of 

Snodgrass Mountain, Gunnison County, Colorado 

by Rex L. Baum, U.S. Geological Survey, Denver, Colorado 

ABSTRACT 

Part of the proposed expansion of ski facilities at Crested Butte Mountain Resort, Gunnison 

County, Colorado, is in an area underlain by landslide deposits that are on the southeast side of 

Snodgrass Mountain. Except for localized movement, the landslides do not appear to be moving 

at present or to have moved in the past several decades. Shallow sliding and debris flows have 

occurred in similar materials nearby and are likely to occur in the landslide deposits during the 

50-100 year life of the proposed facilities. Hazards related to debris flow, shallow slumping, and 

expansive soils in the deposits can be reduced by appropriate engineering and remedial 

measures but maintenance for the proposed facility may become costly. Snow making is likely to 

aggravate the hazards of shallow slumping, deep-seated sliding, and debris flow. Reactivation 

and deep-seated movement of a 1.6-million-m3 slide at the east side of the deposits would 

damage or destroy a proposed gondola, ski lift N-3, and related facilities. Moving the gondola 

and lift off the slide and prohibiting snow making on the slide will protect the gondola and lift and 

reduce the chances of debris-flow damage to a proposed development near the toe of the slide. 

Insufficient data are available to assess the current or future stability of the landslides or to 

evaluate possible mitigation strategies; detailed stability analyses are needed before developing 

any facilities on the landslide deposits. 

INTRODUCTION 

Crested Butte Mountain Resort has 

proposed to expand and develop new ski 

facilities on Snodgrass Mountain, 6 km north 

of the town of Crested Butte, Gunnison 

County, Colorado. The proposal includes a 

gondola, ski lifts, ski runs, roads, utilities, 

and a village in the valley between Crested 

Butte (mountain) and Snodgrass Mountain 

(also called Crested Butte North in some 

documents related to the proposed 

development). Much of Snodgrass 

Mountain is within the Gunnison National 

Forest, but its proximity to the resort town of 

Mount Crested Butte has generated 

considerable public interest in the 

development and its potential environmental 

impact. 

The National Environmental Policy Act 

requires an environmental impact 

assessment for the proposed development. 

As part of this assessment, two private 

contractors have prepared reports on 

geologic hazards in the area of the 

proposed development (Resource 

Consultants and Engineers (RCE), 1995; 

Irish, 1996). Both reports recognized and 

discussed hazards related to expansive 

soils, rock fall, soil creep, and shallow 

landslides. Both also recognized large 

landslide deposits on the southeast side of 

Snodgrass Mountain (Sec. 14, 15, and 23, 

T.13 S., R. 86 W.), but they differed in their 

interpretations of the extent, depth, age, 

probability of reactivation of the deposits, 

and the degree of hazard the deposits pose 

to the lifts, the gondola, and other facilities 

(figs. 1A and 1B). 

As a result of the differing 

interpretations of RCE (1995) and Irish 

(1996), the U.S. Forest Service sought an 

independent opinion on the landslides from 

the U.S. Geological Survey. These large 

landslides and the hazards they pose are 

the subject of this report. The USGS was 

asked to review the previous reports and 

evaluate the stability of the southeast slope 

of Snodgrass Mountain. The evaluation was 

to consider the impact of water added to the 

slope as a result of snow-making 

operations, the effects of and hazard to skiarea development (lift towers, roads, 

utilities, etc.), the hazards to proposed 

commercial real estate development at the 

1
foot of the mountain, and the desire of the 

local community to preserve environmental 

values (view, etc.) that would be destroyed 

in the event of major slope movements. 

I visited the southeast slope of 

Snodgrass Mountain, Gunnison County, 

Colorado, on August 20 and 21, 1996. 

Daryl Gusey, geologist, and Jeff Burch, 

planner, (both USFS) accompanied me in 

the field on the afternoon of August 20, and 

Mr. Burch accompanied me on August 21. 

The field investigation consisted of two 

traverses (fig. 2) through the site to examine 

geologic evidence for past or present slope 

movement. We also observed the landslide 

features from an elevated point on Crested 

Butte. I studied published geologic maps 

and several sets of aerial photographs, 

including color photographs by the USFS 

1988, black-and-white photographs taken in 

1958 and 1973, and false-color infrared 

photographs taken by NASA in 1975. This 

report briefly reviews previous work relevant 

to slope stability at the site, documents my 

own observations, and assesses the 

hazards in relation to the proposed 

development. 

PREVIOUS WORK 

The Colorado Geological Survey 

conducted reconnaissance mapping of 

geologic hazards in the Crested Butte area 

(Soule, 1976). The mapping identified a 

large area of landsliding on the southeast 

side of Snodgrass Mountain. A photograph 

in the report records evidence of recent 

landslide activity south of the study area 

(Soule, 1976, fig. 8). Gaskill and others 

(1991) mapped the same large landslide 

complex in considerable detail. Their map 

delineates the extent of the deposits, scarps 

and other landslide features, and slump 

blocks of Mancos Shale within the slide 

complex. 

Summary of RCE report--Resource 

Consultants and Engineers (RCE, 1995) 

was awarded the investigation of geologic 

hazards (including identification, 

assessment, and mitigation) for the 

proposed expansion of Crested Butte 

Resort. Their investigation consisted of field 

mapping, interpretation of aerial 

photographs, and five borings in landslide 

deposits and their supposed source area on 

the southeast side of Snodgrass Mountain 

(fig 1A). RCE (1995) identified two large 

historic1 landslides on the south side of 

Snodgrass Mountain (fig. 1A). The East 

Slide (fig. 1A) was considered the oldest 

and initiation of the West Slide was 

attributed to drag by the East Slide. The 

supposed source area of the East Slide, 

which extended downslope from the 

secondary summit of Snodgrass Mountain 

to about boring 2, was considered relatively 

stable (fig. 1A). Lifts N-3, N-5, N-6, and the 

gondola cross the landslide deposits or 

supposed source areas. RCE (1995) also 

mentioned a recent landslide, south of the 

permit area, that is in the same materials as 

the two large slides in the permit area. 

The subsurface investigation showed 

the presence of medium-dense sands in the 

supposed source area of the East Slide (fig. 

1A) and stiff clays in the slide deposits 

(RCE, 1995). The borings were made with 

15-cm-diameter, hollow-stem augers and 

each boring was drilled to refusal (table 1). 

The standard penetration test was 

performed at approximately 1.5 m intervals 

and samples were collected but no index 

properties or strength measurements were 

reported. Borings 1 and 2 (fig. 1A) passed 

through clayey sands with gravel- and 

cobble-sized fragments of shale and granitic 

rock (quartz monzonite porphyry). Both 

borings terminated on granitic rock assumed 

to be in place, 7.2-8.7 m below the ground 

surface (table 1). Blow counts generally 

were consistent with a medium density for 

the clayey sand. 

Borings 3, 4, and 5 passed through 

low-plasticity sandy clay of stiff to very stiff 

consistency and weathered shale (fig. 1A). 

All three terminated in hard shale that 

appears to be in place (table 1). In boring 3, 

fragments of granitic rock were present in 

the clay to a depth of at least 14.2 m and 

shale fragments were present in the clay 

below a depth of about 6.1 m. Boring 4 

passed through low plasticity clay with 

 

1The use of historic in the RCE (1995) 

report is confusing; the report indicates that 

the East Slide moved initially after 

Pleistocene glaciers receded and that failure 

is still occurring locally. However, the USGS 

is unaware of any historic accounts of 

movements of these slides. 

2
fragments of weathered shale of 18.7 m 

(granitic rock fragments were also present to 

a depth of 15.7 m). Weathered shale was 

present below 18.7 m to the bottom of the 

boring. Boring 5 passed through sandy clay 

containing weathered shale fragments to a 

depth of 16.7 m , where a buried soil 

containing organic matter and charred wood 

fragments was present. Sandy clay 

containing fragments of granitic rock was 

present below the buried soil. Weathered 

shale was present from 20 m to the bottom 

of the boring. 

Ground water was present in the slide 

deposits (table 1, borings 3, 4, and 5), but 

not in the supposed source area (table 1, 

borings 1 and 2). Piezometers were 

installed in borings 3, 4, and 5 to monitor 

ground water in the slide (fig. 1A). The 

borings, which were drilled in October of 

1994, showed evidence for a high water 

table in the slide deposits that persists into 

autumn (table 1). RCE (1995) noted many 

wetlands on the slides and that several 

surface drainage channels head at the base 

of scarps. The wetlands and heads of the 

channels are consistent with a high 

(possibly perched) water table in the slide 

deposits. 

Table 1. Summary of bore-hole data for the East Slide of Figure 1A (RCE, 1995) 

[Approximate boring locations shown in figure 1A.] 

Boring Depth Depth 

of 

Water 

Table 

Depth 

of 

Piezometer 

Comments 

Meters Meters Meters 

1 - - - - 7.2 none none - - - - 

2A - - - 7.6 none none - - - - 

2B- - - 

- 

7.2 none none 1.5 m east of 2A 

2C - - - 8.7 none none 2.4 m west of 2A 

3 - - - - 19.4 12.8 19.4 - - - - 

4 - - - - 30.6 3.5 30.5 - - - - 

5 - - - - 24.5 9.4 24.4 Buried soil with charred wood fragments at 16.8 m 

3
RCE (1995) concluded that the proposed development could destabilize the slide deposits 

(roughly the downhill half of the East Slide and the downhill two-thirds of the West Slide, fig. 1A) 

and that planned snow-making could contribute to failure by raising the water table. The potential 

hazards related to failure of the deposits included shallow creep, debris flow, small secondary 

slides, settlements, and slow, deep-seated movements. RCE (1995) proposed mitigating the 

hazards by moving the gondola and related structures off the slide to the stable ridge to the east. 

Alternatively, if moving the gondola were not practical, then RCE (1995) recommended providing 

subsurface horizontal drains and monitoring ground water, surface monuments, and 

inclinometers. Surface monuments have been installed and are being monitored (Jeff Burch, 

USFS, oral commun., 1996) 

Summary of Irish report.--Mr. R.J. Irish visited the site June 3 and 4, 1996 and conducted 

studies of existing reports and aerial photographs of the south end of Snodgrass Mountain (Irish, 

1996). The objectives of his study were to describe geologic conditions, with particular reference 

to geologic hazards, assess the risk related to any perceived hazards, and suggest mitigative 

measures for the hazards. 

Irish (1996) recognized two ancient or pre-historic landslide complexes on the southeast 

side of Snodgrass Mountain (fig. 1B); however, he interpreted their extent and depth differently 

than RCE (1995). Irish (1996) recognized a West Slide (fig. 1B) that he classified as a blockslide complex. He asserted that a Base Hill of in-place Mancos Shale buttresses the West Slide 

(fig. 1B). His East Slide (fig. 1B) is a thin (2.7 m) mud flow and single rotational block in the 

alignment of the gondola and lift N3. On the basis of the following observations and ideas, Irish 

(1996) concluded that the probability of catastrophic reactivation of either slide complex was low: 

(1) No open cracks or fresh scarps were observed and the landslide features, particularly of the 

West Slide (fig. 1B), have been rounded by erosion. (2) The Base Hill buttresses the West Slide 

(fig. 1B). (3) The East Slide (mud-flow complex), appears to be thin2. (4) The conditions thought 

to trigger the slides (glacial erosion and high precipitation) have changed or ceased. (5) Work by 

others (Kirkham and Rogers, 1981; Algermissen, 1983) indicates low probability of significant 

earthquake acceleration during the expected life of the project. Irish (1996) assigned low 

probability to small failures also, although he noted the presence of many small slumps and flows 

in the West Slide complex and uphill from the East Slide (fig. 1B). He concluded that more small 

slides can occur, especially if poor construction practices are followed. 

Irish (1996) recommended that the hazards could be mitigated by sensible construction 

practices, including minimizing cut-and-fill construction, providing drainage to prevent ponding of 

water, revegetation of slopes after construction, and maintaining forests as much as possible. 

Although he did not expect the towers to affect the stability of the slides, Irish (1996) noted that 

the gondola and lift N-3 could be relocated to the east or west to avoid any potential problems 

related to putting them on the East Slide (fig. 1B). He did not expect problems for lift N-5 unless 

poor construction practices changed conditions. Irish (1996) stated that no houses or other major 

buildings should be placed on the slides and that he did not expect snow-making to affect stability 

of the slides. 

SITE GEOLOGY 

Gaskill and others (1991) have documented the geology of Snodgrass Mountain. It is 

capped by a 300-m-thick laccolith of quartz monzonite or granodiorite that intruded the Upper 

Cretaceous Mancos Shale. Mancos Shale underlies the lower slopes of the mountain. Glacial 

activity has modified the slopes and left deposits of moraine on the sides of the mountain. 

 

2Irish (1996) reinterpreted the boring logs of RCE (1995) and concluded that the East Slide was 

only about 2.7 m thick at boring 4 and underlain by in-place shale. This reinterpretation is 

inconsistent with the presence of the fragments of granitic rock as deep as 15.7 m in boring 4 and 

the buried soil, wood fragments, and organic matter found at 16.8 m in boring 5. 

4
Colluvial deposits cover much of the east and west sides of the mountain. Extensive landslide 

deposits occupy a crudely semicircular basin at the southeast side and blanket slopes on the 

south side of the mountain (fig. 2). The topography of landslide deposits within the basin is 

stepped. Scarps on the sides of Snodgrass Mountain indicate shallow slumping in the colluvial, 

glacial, and landslide deposits (Gaskill and others, 1991). 

DESCRIPTION OF THE LANDSLIDES 

Based on examination in the field and on aerial photographs, the slide deposits in the basin 

at the southeast end of Snodgrass Mountain can be divided into three main units, the Slump 

Block, the West Slide and the East Slide (fig. 2). Movement of all three units was toward the 

southeast. 

A low, rounded hill at the base of the complex constitutes the Slump Block. This hill is not 

in-place bedrock as asserted by Irish (1996), but rather a displaced mass that slid into its present 

position from a source area (evidenced by an eroded scarp) directly upslope. The surface of the 

hill is hummocky, and in aerial photographs the hill has a dark, slightly mottled tone that matches 

the tone of surrounding landslide debris and is different from the light, strongly mottled tone of 

nearby shale hills to the south and east. A 70-m-high, relatively steep scarp slope surrounds the 

Slump Block and marks its source area (fig. 2). Field examination confirmed a landslide origin for 

the Slump Block. The surface of the Slump Block, particularly south of the summit, consists of 

rounded hummocks, and the drainage is somewhat irregular. This contrasts sharply with the 

smooth slopes and dendritic drainage of the hills to the south and east. Weathered shale crops 

out locally on these hills, which have a thin, spotty cover of till (Gaskill and others, 1991). 

A slide complex upslope (to the west and north) from the Slump Block constitutes the West 

Slide (fig. 2). The head of the West Slide is at the base of an arcuate scarp at the south end of 

the Snodgrass laccolith. Trees obscure much of the scarp and upper part of the deposits on the 

West Slide, however, parts of small benches and scarps are visible through the trees. The 

ground on the West Slide is hummocky, and drainage is irregular; intermittent ponds occur in 

closed depressions (fig. 2). 

A slump-earth-flow complex at the east edge of the basin constitutes the East Slide (fig. 2). 

Two high, arcuate scarps (related to slumping) are at the top of the complex, and the surface of 

the earth flow, downhill from the scarps, is stepped and hummocky. The East Slide is draped 

over the Slump Block and 70-m-high scarp (fig. 2). 

Dimensions.--The Slump Block has gentle (<10 percent) reversed (west-northwest) slopes 

between its west boundary and summit; slopes range from 25 to 40 percent on the downhill (east 

and south) faces. The Slump Block measures 580 m from head (at base of the 70-m high scarp) 

to toe and 700 m from north flank to south flank (including the area beneath the East Slide). The 

West Slide (fig. 2) has an average slope of 28 percent; slopes range from 25 to 40 percent on the 

70-m-high scarp, 13 to 20 percent on the gently sloping ground above the scarp, and 25 to 60 

percent near the head. The West Slide is 700 m wide from northwest flank to southeast flank 

and 900 m long from head to toe (at west edge of the Slump Block). The East Slide (fig. 2) 

slopes 22 percent; slopes locally range from 100 percent near the head to 11 percent in a gently 

sloping area near the toe. The slide has a volume of 1.6-million m3 based on a length of 800 m, 

width of 200 m, and minimum average thickness of 10 m. The minimum average thickness is 

estimated from the difference in elevation between the East Slide and ground at either side (fig. 

2). Boring 5 (fig. 1A) (RCE, 1995), in the toe of the East Slide (fig. 2), turned up charred wood at 

a depth of 16.8 m and "granitic sandy gravel," which is not native to the underlying Mancos 

Shale, as deep as 20 m. Thus the East Slide or a combination of the East Slide and underlying 

Slump Block may be as much as 20 m thick; no data are available to determine the thickness of 

the West Slide (fig. 2). A recent slide on the south end of Snodgrass Mountain slopes 39 

percent, and is about 600 m long, 200 m wide, and probably a few meters thick (fig. 2). 

5
Ages.--Absolute ages of the three units are unknown, but the East Slide is younger than 

the Slump Block and West Slide (fig. 2). The East Slide overlaps the Slump Block. The West 

Slide and Slump Block are more deeply eroded and have more rounded features than the East 

Slide. 

The Slump Block, East Slide, and West Slide (fig. 2) have not moved significantly in historic 

times. No signs of recent changes in the slide deposits are evident between photographs 

spanning 30 years. The vegetation is undisturbed, and the same areas that are bare on the old 

slide deposits and scarps in the 1958 photographs are bare in the 1988 photographs. We found 

no field evidence of recent activity such as fresh scarps or open cracks; however, despite the 

lack of evidence for significant movement, the slides can still be marginally active because small 

(sub-centimeter) annual movements are known to occur in some slides without cracks or other 

visible evidence of movement being preserved (Fleming and Johnson, 1994). 

The recent slide on the south slope (fig. 2) appears to have been active in the past 40 

years. Boundaries of the recent slide appear to be sharp and barren, as if it were active, in the 

1958 photographs. The same boundaries in the 1988 photographs appear subdued and partly 

overgrown. Also, a scar in the lower part of the slide has distinct head and flank scarps and 

exposes fresh landslide debris. The area occupied by the scar appeared to be unvegetated in 

the 1988 photographs, but no scarps were apparent. 

LANDSLIDE HAZARDS 

Several geologic hazards, including expansive soil, debris flow, shallow sliding, and deepseated failure must be considered in developing ski facilities on or near the landslide deposits. 

Expansive soils have caused damage to buildings at Crested Butte Mountain Resort (D.J. 

Varnes, USGS, oral commun., 1996) and have been discussed by RCE (1995) and Irish (1996). 

Debris flows can be triggered during times of high rainfall or rapid melting of natural or 

artificial snow. A debris flow that occurred in the spring of 1996 on the north side of Crested 

Butte (J. Burch, oral commun., 1996) demonstrates that debris flows do occur on similar slopes 

under existing conditions. Debris flows originating in the slide deposits can damage access 

roads, utilities, or the proposed development in the valley between Crested Butte and Snodgrass 

Mountain. In particular, debris flows originating on or near the East Slide (fig. 2) can damage the 

proposed development at the foot of Snodgrass Mountain. Use of artificial snow on the East 

Slide (fig. 2) may increase the probability of debris flow there. The occurrence of debris flows is 

highly likely during the life of the facility, given the recent occurrence. 

Shallow sliding or slumping can damage access roads, utilities, towers of the gondola, or 

towers of lifts N-3, N-5, and the south end of lift N-6. The recent activity of the shallow slide on 

the south side of Snodgrass Mountain demonstrates that such slides can and do occur under 

existing conditions. Slopes on the West Slide, Slump Block, and East Slide (fig. 2) are locally as 

steep as the recent slide (fig. 2). The lower 2/3 of lift N-5 is in the area of scarps mapped by 

Gaskill and others (1991). 

Deep-seated failure and renewed movement of the entire landslide deposit (i.e. the East 

Slide, West Slide, and Slump Block, fig. 2) would threaten all the proposed facilities in the area 

(i.e. lifts N-3, N-5, N-6, the gondola ,and the proposed development). Such movement might 

occur if the Slump Block is disturbed by excavation or erosion. The Slump Block appears to 

buttress higher deposits of the West Slide (fig. 2) and secure them against massive failure. 

Excavation of the toe or top of the Slump Block will remove part of the buttress load and increase 

the chances of failure. Downward erosion of the stream channel at the toe of the Slump Block 

(related either to a basin-wide episode of incision or a local increase in discharge) will increase 

the height of the slope and tend to destabilize the Slump Block. 

6
Deep-seated failure resulting in reactivation of the East Slide (fig. 2) can damage or destroy 

the gondola and lift N-3. Reactivation and deep-seated movement of the East Slide is more likely 

than reactivation of the entire landslide complex; the East Slide rests on top of the Slump Block 

(fig. 2). Slides that were similar in geometry and degree of erosion of surface features were 

reactivated by rapid melting of a heavy snowpack during 1983 in central Utah (Baum and 

Fleming, 1989). The 1.6-million-m3 (or greater) East Slide (fig. 2) is too large to remove and any 

other methods of stabilizing it will be costly. Avoidance of any development or snow-making on 

the East Slide (fig. 2) may be the safest and least expensive option for reducing the potential 

losses. Site-specific studies are needed to evaluate other possible mitigation options. 

The preceding paragraphs describe potential landslide and debris-flow events and related 

hazards to the proposed ski facilities for the southeast side of Snodgrass Mountain; however, the 

paragraphs contain little information on the probability of the events occurring. Estimating the 

probability of landslide occurrence is speculative, particularly when the estimate is based on 

qualitative data alone. Quantitative data needed to perform stability analysis of the landslide 

deposits and estimate the probability of their reactivation are lacking in the reports of RCE (1995) 

and Irish (1996). These data include, at a minimum, relevant shear-strength, geometric 

(topography and thickness), and pore-pressure measurements of the landslide deposits. 

Detailed site investigation and engineering analysis are needed to predict whether the slide 

deposits will remain stable during the life of the proposed facilities. Such investigation and 

analysis should be required before any facilities can be constructed on the landslide deposits. 

CONCLUSIONS 

The ski facilities proposed for the southeast side of Snodgrass Mountain (Crested Butte 

North) are subject to several geologic hazards inherent to development on large landslide 

deposits. Safe and economic development of facilities on the West Slide and Slump Block (fig. 2) 

will require detailed, site-specific studies and adequate engineering to reduce damage from 

expansive soils, debris flows, and shallow sliding or slumping. In addition to damage from these, 

facilities on and downslope from the East Slide (fig. 2) are also subject to possible damage or 

destruction by deep-seated sliding. Detailed field investigation and stability analysis are required 

to determine whether the East Slide is sufficiently stable to support the proposed facilities. Given 

the magnitude of the investment to develop the ski facilities and the potential losses due to deepseated failure, detailed subsurface investigation and stability analysis should also be undertaken 

for the West Slide and Slump Block (fig. 2) before going ahead with development of any 

proposed facilities on or near the southeast side of Snodgrass Mountain. 

REFERENCES 

Algermissen, S.T., 1983, An introduction to the seismicity of the United States: Earthquake 

Engineering Research Institute, Berkeley, California., 148 p. 

Baum, R.L., and Fleming, R.W., 1989, Landslides and debris flows in Ephraim Canyon, central 

Utah, chap. C of Landslide processes in Utah--Observation and theory: U.S. Geological 

Survey Bulletin 1842, p. C1-C12, 1 oversize plate. 

Fleming, R.W., and Johnson, A.M., 1994, Landslides in colluvium: U.S. Geological Survey 

Bulletin 2059-B, 24 p. 

Gaskill, D.L., Mutschler, F.E., Kramer, J.H., Thomas, J.A., and Zahony, S.G., 1991, Geologic 

Map of the Gothic Quadrangle, Gunnison County, Colorado: U.S. Geological Survey 

Geologic Quadrangle Map GQ-1689, 1:24,000. 

Irish, R.J., 1996, Geologic Hazard Study zones 3A and 3B Crested Butte Mountain Resort 

Expansion Area, Snodgrass Mountain, Gunnison County, Colorado: Denver, Colorado, 

7
R.J. Irish, Consulting Engineering Geologist, Inc., Report to Pioneer Environmental 

Services, Inc., Logan, Utah, June 12, 14 p. 

Kirkham, R.A., and Rogers, W.P., 1981, Earthquake potential in Colorado--A preliminary 

evaluation: Colorado Geological Survey Bulletin 43, 171 p. 

RCE, 1995, Geologic hazard assessment and mitigation planning for Crested Butte Mountain 

Resort, Gunnison County, Colorado: Fort Collins, Colorado, Resource Consultants and 

Engineers, Division Ayres Associates, Report to Pioneer Environmental Services, Inc., 

Logan, Utah, February 16, 40 p.+ appendix, 2 oversize plates. 

Soule, J.M., 1976, Geologic hazards in the Crested Butte-Gunnison area, Gunnison County, 

Colorado: Colorado Geological Survey Information Series, no. 5, 34 p. 

8