GEOLOGICAL SURVEY CIRCULAR 689 

Effects of the 

May 5-6, 1 973, Storm 

in the Greater Denver Area, 

Colorado 

Effects of the 

May 5-6, 1973, Storm 

in the Greater Denver Area, 

Colorado 

By Wallace R. Hansen 

GEOLOGICAL SURVEY CIRCULAR 689 

1973 
United States Department of the Interior 

ROGERS C. B. MORTON, Secretary 

Geological Survey 

V. E. McKelvey, Director 

Free on application to the U.S. Geological Survey, National Center, Reston, Va. 22092 
CONTENTS 

Page Page 

Abstract-------------------------------------------------------------------------- 1 Geologic effects of the storm- Continued 

Introduction ___________________________________________________________________ _ 1 Scour ........ ---------------------------------------------------------------- 6 

Purpose of the report ___________________________________________ _ 2 Sedimentation·-------------------------------------------------------· 10 

Place names------------------------------------------------------------ 2 Mass wastage.·------------------------------------------------------·- 11 

Acknowledgments _________________________________________________ _ 2 Slumps and earthflows__________________________________ 13 

Inundation _____________________________________________________________________ _ 4 Mudflows·--------------------------------------------------------· 16 

Overwhelming of artificial drainage systems 4 Rockfalls------------------·--·-----------------------------------· 17 

Problems with canals and ditches ______________________ _ 4 Toward coping with future storms_____________________________ 18 

Geologic effects of the storm---------------------------------------- 6 References cited·------------------·----------------------------·------------ 20 

ILLUSTRATIONS 

Page 

FIGURE 1. Location map of the Greater Denver area·-----------------------------------------------------·-·-----------------------------------------· 3 

2-10. Photographs: 

2. Flooding at East Jefferson Avenue and South Emerson Street, Englewood__________________________ 5 

3. Flooding at Kennys Gulch at 21st and Ford Streets, Golden·----------------·-----------------·--------------- 6 

4. Highline Canal flooding across Bible Park.·-----·-----------------------------------------------------------------·····------ 7 

5. View of 15th Street Bridge shortly after collapse ........ -------------------·-·---·------------------------------------· 8 

6. Severe bank scour by Bear Creek. ..... _______________________________________________ .............................................. 9 

7. Scour by Mount Vern on Creek ............ ----------·-----------·--------·-------------·---·-------·-·-----------·----------·-·-·-·--·- 10 

8. Scour by West Creek ............................ -----------·---------------------------------------------·--·-----·----------------·------·-- 10 

9. South Platte River just west of Brighton ......................................................... ____________________________ 11 

10. Overbank sediments deposited along Mcintyre Gulch at Holland Street--------·-·--------------------- 12 

11. Block diagram illustrating form and nomenclature of a landslide·--------------------------·-----------------------·-----· 12 

12. Block diagrams shewing landslide types common in the western part of the G1·eater Denver area 13 

13-19. Photographs: 

13. Debris-mudflow blocking Hogback Road, 1 mile north of Monison .. ·------------------------·---------· 14 

14. Landslide in Denver Formation on old Colorado Highway 58 ...... --------------·---------------------------· 15 

15. Debris slide on eastbound exit ramp of Interstate 70 at Genessee Mountain________________________ 15 

16. Small slump on Boulder County road 2 miles west of Jefferson County Airport.................. 16 

17. Slum:t>-earthflow on State Highway 121 about three-fourths mile south of Broomfield 

interchange·---··-·-·-·---·-------------------------------------·---------------·------------------·------------·----------------------------- 16 

18. Rockfall on Interstate 70, 2 miles west of Bergen Park interchange··-----·-------------------------·- 17 

19. Gullying on a steep hillside previously denuded of vegetation and topsoiL___________________________ 19 

III 

Effects of the May 5-6, 1973, Storm in the 

Greater Denver Area, Colorado 

By Wallace R. Hansen 

ABSTRACT 

Rain began falling on the Greater Denver area the 

evening of Saturday, May 5, 1973, and continued 

through most of Sunday, May 6. Below about 7,000 feet 

altitude, the precipitation was mostly rain; above that 

altitude, it was mostly snow. Although the rate of fall 

was moderate, at least 4 inches of rain or as much as 

4 feet of snow accumulated in some places. Sustained 

precipitation falling at a moderate rate thoroughly saturated the ground and by midday Sunday sent most of 

the smaller streams into flood stage. The South Platte 

River and its major tributaries began to flood by late 

Sunday evening and early Monday morning. 

Geologic and hydrologic processes activated by the 

May 5-6 storm caused extensive damage to lands and 

to manmade structures in the Greater Denver area. 

Damage was generally most intense in areas where 

man had modified the landscape- by channel constrictions, paving, stripping of vegetation and topsoil, and 

oversteepening of hillslopes. Roads, bridges, culverts, 

dams, canals, and the like were damaged or destroyed 

by erosion and sedimentation. Streambanks and structures along them were scoured. Thousands of acres of 

croplands, pasture, and developed urban lands were 

coated with mud and sand. Flooding was intensified by 

inadequate storm sewers, blocked drains, and obstructed 

drainage courses. Saturation of hillslopes along the 

Front Range caused rockfalls, landslides, and mudflows 

as far west as Berthoud Pass. Greater attention to geologic conditions in land-use planning, design, and construction would minimize storm damage in the future. 

INTRODUCTION 

The Greater Denver area has had a long history of intensive rainstorms and infrequent but 

destructive floods. Though people are prone to 

forget, memories were refreshed by the storm 

of May 5-6, 1973, and the events that followed. 

The weather forecast for Sunday, May 6, 

called for cooler temperatures, considerable 

cloudiness, and a chance of showers. Few people, therefore, took much note of the onset of 

1 

a light drizzle late Saturday evening of May 5, 

but by early Sunday morning, the magnitude of 

the area-wide storm was becoming apparent to 

all. By midday, many small streams were flooding over their banks, reservoirs were spilling, 

and canals were overflowing. The South Platte 

River and its major tributaries were rising 

ominously toward peak discharges late Sunday 

night and early Monday morning. 

Although the rate of precipitation on Sunday was not heavy by meteorological criteria, 

the long duration of steady rain and the total 

amounts in some places were exceptional. Some 

backyard rain gages showed more than 4 inches 

of moisture. The 24-hour depth measurements 

at rainfall-runoff stations of the U.S. Geological 

Survey ranged from 2.03 inches in Northglenn 

to 4.38 inches in northeast Denver (Ducret and 

Hansen, 1973, table 2). In northeast Denver a 

100-year record was set for sustained precipitation for a 24-hour period. 

Above an altitude of about 7,000 feet, most 

of the precipitation fell as snow. Twenty inches 

of heavy wet snow fell over broad areas of the 

mountains, and as much as 42 inches was reported at Black Mountain, west of Conifer (The 

Denver Post, May 9, 1973). Precipitation in the 

form of snow retarded runoff in these areas 

and, therefore, diminished the peak of flood discharge. Conversely, infiltration of moisture into 

the ground was increased, and, consequently, so 

was the potential for landsliding. Had all the 

moisture in the mountains fallen as rain, runoff would have been more rapid, and flooding 

would have been more intense, but infiltration 

would have been less, and there would have 

been fewer landslides. 
In terms of local runoff in the metropolitan 

area of Denver, especially with respect to the 

smaller tributaries of the South Platte River, 

the May 5-6 storm was fairly commonplace. 

Residents can expect similar occurrences at 

fairly frequent intervals. Peak-flow recurrence 

intervals ranged from only 3 years at some sites 

to 20 years or more at others (Ducret and Hansen, 1973, tables 3, 4). The flooding of the South 

Platte itself was essentially a 50-year event. 

In terms of geologic effects, such as scour 

and especially mass wastage, the storm was unusual- probably because of the thorough saturation of the gtound that resulted from the 

moderate rate of sustained precipitation. In 

nearly 25 years of residence in the area, the 

author has not seen its equal. 

The rainfall and flooding that accompanied 

the storm had widespread geologic and hydrologic effects, brought about through erosion, 

sediment transport and deposition, and slope 

failure. By "geologic effects" are meant the 

quasi-permanent changes, however small, in the 

character or form of the rocks, soils, and physical geography that together make up the landscape. Many of these effects were of a small 

scale compared to the gross geologic setting of 

the area, but they provided dramatic evidence 

of the irresistibility of geologic processes, and 

they accounted for a substantial part of the 

damage to the works of man. Thus, the deposition of a few inches of sediment on a few acres 

of ground, or the erosion of a few cubic yards 

of river bank, might be of little obvious note in 

the geologic scheme of things but might damage or destroy cropland or a section of highway 

worth many thousands of dollars. Similarly, the 

undercutting of the footing of a single bridge 

pier might destroy the whole bridge and necessitate the expenditure of many thousands of 

dollars for replacement or repair. A small landslide might jeopardize the integrity of a structure worth a large sum of money. Geologic 

processes set into motion by the storm thus 

caused extensive damage to lands and engineering works throughout the Greater Denver area 

and the South Platte River flood plain. Damaged roads, bridges, dams, canals, and the like, 

were the chief losses in the public sector. 

2 

PURPOSE OF THE REPORT 

Because of the rapid present and projected 

growth of Greater Denver, problems related to 

storm drainage are likely to increase in scale 

and frequency in the future. Nat ural processes, 

once set into motion, may be very difficult to 

control, but man can, with foreknowledge, prevent or avoid many direct encounters. He can 

sometimes circumvent the effects of a major 

storm, and he can take steps to minimize the 

causes and effects of inundation. The first step 

is to assess and attempt to understand the 

causes of past storm damage. 

This report, therefore, presents a capsule 

summary of the principal effects of the storm 

of May 5-6, 1973, in the hope that a broader 

public understanding of the effects of a past 

storm will lead to a greater awareness of the 

potential effects of future storms and to more 

effective measures to forestall storm damages 

in the future. 

PLACE NAMES 

Dozens of local place names are variously 

mentioned in this report. Most of these names 

are plotted on the location map (fig. 1), but to 

so identify all of them on a map of this size is 

not feasible. Such features as roads and street 

intersections are readily located from city maps 

and directories published by private and public 

agencies, including the U.S. Geological Survey's 

topographic maps at a scale of 1:24,000 (1 inch 

to 2,000 feet), which are available at map-sales 

outlets. Oil-company road maps of Denver and 

vicinity are available at most gasoline service 

stations and are very useful references. One or 

more of these sources can be consulted to locate 

place names closely enough for most purposes. 

ACKNOWLEDGMENTS 

Much information in this report was provided by Geological Survey colleagues who investigated flood effects in various parts of the 

Greater Denver area immediately after the 

storm; included were Roger B. Colton, Eugene 

R. Hampton, Robert M. Lindvall, John 0. Maberry, Edward E. McGregor, and Howard E. 

Simpson. Local newspaper accounts have been 

freely utilized, also. David J. Varnes kindly 

loaned the original drawing from his diagram 

showing the nomenclature of a landslide 
r I ~OliLDER JEFFERSON C~ CO -

I Rocky 

Flats 

I 

I 

I 

I 

WELD CO 

ARAPAHOE CO 

FIGURE 1.- Location map of the Greater Denver area. 

3 

AREA/ 

OF MAP 

INDEX MAP OF 

COLORADO 

ARAPAHOE CO 

--DOUGLAS CoT 

I 

I 

I 

I 

I 

I 

I 

I 
(Varnes, 1958, pl. 1). The well-done sketches 

of rockfall, slump, debris slide, and earthflow 

were drawn by Natalie J. Miller of Menlo Park, 

Calif., and were first published by Tor H. Nilsen (1972). A companion report, dealing with 

the rainfall-runoff frequencies of the storm 

(Ducret and Hansen, 1973), has been published 

by the Urban Drainage and Flood Control District (Denver) . 

INUNDATION 

A large part of the total storm damage was 

caused simply by inundation, with all its costly 

side effects. In the private..· sector, inundation 

was the chief cause of loss. Many homes, commercial buildings, warehouses, outbuildings, 

utilities, and railroad rolling stock and yards 

received damage. Side effects included the related spoilage of myriad household goods and 

other personal properties, waterlogging of croplands and pastures, the drowning of livestock, 

and the indirect loss of income of the flood victims. The list is endless. 

Inundation resulted not only from overbank 

flooding of streams but also from the backup 

of water behind obstructions at bridges and culverts along tributaries that otherwise would 

not have gone out of their banks, or along artificial drainages that had not been intended to 

accommodate more than moderate volumes of 

storm runoff. Much flooding was aggravated 

by intensified drainage in urban areas where 

roofs, driveways, walks, streets, parking lots, 

and other impermeable surfaces contributed to 

high peak runoff. 

The main stem of the South Platte River was 

out of its banks from Douglas County to the 

Nebraska State line, having crested in Denver 

late Sunday night, May 6, and early Monday 

morning, May 7. At peak discharge, its flood 

attained an approximate recurrence interval of 

50 years at Littleton, 1.1 X 50 years at Denver 

below the mouth of Cherry Creek, and 1.4 X 50 

years at Henderson (Ducret and Hansen, 1973, 

table 3). Flooding along the South Platte in the 

metropolitan area was heaviest in the vicinity 

of Chatfield Dam (under construction in 1973) 

and Centennial Racetrack in Littleton; in the 

vicinity of West Alameda A venue and South 

Santa Fe Drive in the Westwood section of Denver, where Interstate 25 Highway was closed to 

traffic for several days ; in the lower downtown 

4 

area in the vicinity of the railroad yards ; in 

Commerce City; in Henderson; and in Brighton. 

Elsewhere in Greater Denver, urban flooding 

was heavy locally where tributaries went out of 

their banks or backed up behind obstructions 

(fig. 2). In particular, extensive areas in Englewood were inundated by Little Dry Creek, the 

peak discharge of which had an approximate 

recurrence interval of 20 years (Ducret and 

Hansen, 1973, table 4). Many places throughout 

Greater Denver were flooded by overflow from 

canals and ditches. 

OVERWHELMING OF ARTIFICIAL DRAINAGE SYSTEMS 

In many built-up areas artificial drainage 

systems were inadequate to accommodate the 

runoff, and water quickly rose to flood levels 

(fig. 3). Proportionately, the amount of runoff 

that reached trunk drainages in built-up areas 

was much larger than in nonbuilt-up areas of 

equal size, simply because runoff which otherwise would have infiltrated the ground drained 

off totally from impervious roofs, sidewalks, 

streets, gutters, and pavements. Drains designed 

to accommodate modest rainstorms were overwhelmed or blocked with debris, and as tributary drain systems merged, the problem was 

compounded. Many areas, such as much of 

Lakewood, simply lack adequate facilities to 

handle heavy storm runoff (The Lakewood Sentinel, May 10, 1973). Facilities that may have 

been adequate in the past, moreover, were suddenly unable to accommodate the surge of water 

from new subdivisions higher in the watershed. 

As growth continues, smaller and smaller 

storms are able to generate larger and larger 

discharge. 

PROBLEMS WITH CANALS AND DITCHES 

Many irrigation canals and ditches were 

quickly filled to the point of spillage and washout despite efforts to shut them off at the source. 

But the flow of a canal cannot be turned off 

like a water faucet just by closing a headgate 

that is, perhaps, miles away. Canals flow nearly 

along the contour of the ground, and they intercept storm runoff from many minor drainageways that normally carry no water. Highline 

Canal is a good example. It heads at the mouth 

of Platte Canyon and flows northeastward 

across the Greater Denver area to a point in 

Adams County east of the Rocky Mountain Ar-
FIGURE 2. - Flooding at East Jefferson Avenue and South Emerson Street in Englewood, caused by the overflow 

of Little Dry Creek. Denver Post photograph by John Prieto, May 6, 1973. 

senal, intercepting many small drainages en 

route. Highline Canal was out of its banks in 

many places (fig. 4), especially in southeast 

Denver, where many basements were flooded. 

At Wellshire Municipal Golf Course it threatened Skeel Reservoir, which has no spillway 

and nearly overtopped its dam. Downstream at 

the Rocky Mountain Arsenal, overflow from 

the canal and the Montbello ditch breached Upper Derby dam, sent a surge of water into 

Lower Derby Lake, and threatened Irondale, 3 

miles to the northwest. According to Quentin 

Hornback of the Denver Water Board (oral 

commun., relayed by Robert M. Lindvall) many 

small tributaries of the South Platte poured 

water into canals and ditches, such as Highline. 

In Lakewood, much of the flood damage was 

caused by overflowing irrigation ditches. Spillage from Main Reservoir, taking excessive inflow from Welch ditch, flooded West Mississippi 

5 

A venue for 18 hours between South Kipling 

and South Garrison Streets (The Lakewood 

Sentinel, May 10, 1973). Normally, overflow of 

Main Reservoir is handled by Weir Gulch. 

In Edgewater, sluggish drainage from an 

overflowing ditch backed up sewers in a fourblock area near West 20th A venue and Sheridan Boulevard, sent raw sewage into numerous 

basements, and caused the street to be closed 

for several hours. The problem has been recurrent. It was not caused exclusively by the storm, 

but it was aggravated by the storm. The Edgewater Volunteer Fire Department ultimately 

was forced to pump the water and sewage into 

nearby Sloans Lake in order to reopen street 

traffic (The Denver Post, May 9, 1973; The 

Lakewood Sentinel, May 10, 1973). Similar 

sewer backups were reported over wide areas 

of Greater Denver, the cause, for the most part, 

being the same: sanitary sewers were simply 
FIGURE 3. - Flooding along Kennys Gulch at 21st and Ford Streets in Golden. Urban runoff and overflow of Welch 

ditch exceeded capacity of storm drains. Photograph by John R. Keith, May 6, 1973, at height of storm. 

overwhelmed by the backup of water from overflowing ditches and storm sewers. 

Outside the urban area, according to Don 

Svedman, State Deputy Commissioner of Agriculture, farmers and ranchers sustained heavy 

flood losses, partly the result of overfilled 

washed-out irrigation ditches (The Denver 

Post, May 8, 1973). 

GEOLOGIC EFFECTS OF THE STORM 

The processes of erosion, transport, and redeposition of materials by the floodwaters, and 

the infiltration of moisture into the ground -

either directly from precipitation or indirectly 

by lateral soaking from flooded stream courses 

-altered the landscape in many ways. Streambanks and structures along the banks were attacked by scour, and, in many places, were 

destroyed. Thousands of acres of flooded lands 

were coated with mud and sand. Saturated hillsides and streambanks gave way under the 

added weight of the moisture. Locally, rocks 

bounded down hillsides onto roads and highways. 

For discussion purposes, the geologic effects 

of the storm are here grouped by process under 

the three main headings "Scour," "Sedimenta6 

tion," and "Mass Wastage." Scour predominated over other processes in its effects on 

manmade structures and the resultant damage 

costs. Mass wastage-mainly landsliding-was 

widespread in hilly areas, but its economic consequences were much less than those of scour. 

Sedimentation was the least destructive of all 

in the Greater Denver area, although it did 

much damage to croplands downstream along 

the South Platte River. 

SCOUR 

The sediment-carrying capacity of a stream 

increases enormously in flood. As the volume of 

water rises, so does the velocity, and with increased velocity, the carrying capacity increases 

geometrically - the enlarged stream, flowing 

faster, scours its channel and quickly acquires 

a load of sediment. Conversely, the sediment 

carried in flood is quickly dropped when stream 

velocity is reduced. 

Nearly all perennial streams in the area, and 

countless intermittent ones, scoured segments 

of their banks and beds. Scour was a major 

cause of damage along the South Platte itself, 

as well as along its tributaries. Scour was most 

noticeable in cutbanks at the outsides of bends, 

where the force of the current has the most 
FIGURE 4. - Highline Canal out of its banks and flooding across Bible Park in southeast Denver, May 6, 1973. 

Photograph by L. Scott Tucker, executive director, Urban Drainage and Flood Control District (Denver). 

kinetic energy, and along entrenched reaches, 

especially at places where channels had been 

constricted by artificial landfilling along the 

banks. According to Fred Watts, Deputy Director of Public Works for Denver, the South 

Platte "just ate away all of Platte River Drive 

between Yale and Mississippi" (quoted from 

the Rocky Mountain News, May 9, 1973). Along 

this reach the channel of the river had been 

greatly constricted by filled land. Three weeks 

after the storm, the South Platte was still running bankfull and was too high to permit close 

inspection of scour effects along its banks. The 

South Platte had, in fact, surged over its banks 

again on May 22 after having receded to a level 

below flood stage in Denver a week earlier. 

In downtown Denver, the 15th Street Bridge 

across the South Platte River collapsed when 

its center-support pier was undercut by scour 

(fig. 5). Collapse of the bridge, moreover, severed eight telephone cables and disrupted telephone service between downtown Denver and 

7 

northwest Denver, parts of Arvada, Broomfield, 

and Boulder. The four-lane bridge was less than 

10 years old and had survived the 1965 flood 

and the heavy runoff of 1969. According to City 

Engineer Jack Bruce (The Denver Post, May 

7, 1973), it was the bridge least expected to 

fail. When the center pier went out, the bridge 

collapsed inward, trapdoor like, from both 

abutments. 

Although no other bridges failed within the 

city limits of Denver, bridges and culverts were 

among the chief casuaities of the flood elsewhere, and their failures added greatly to the 

cost of the storm. Bridges and culverts are particularly vulnerable because they form channel 

constrictions which increase the velocity and 

the competence of the stream. Bridges and culverts, moreover, tend to increase the severity of 

flooding when dammed or blocked by trapped 

debris. Such blockages backed water into building basements and first-floor levels in many 

parts of the metropolitan area, blocked and 
FIGURE 5.- View of 15th Street Bridge in downtown Denver, shortly after iJs collapse. Center-support pier was 

undercut by scour. Denver Post photograph by John Prieto, May 6, 1973. 

backed up sewers in many places, and extinguished pilot lights and shorted out home furnaces. With these effects in mind, crews from 

the Denver Street, Highways, and Fire Departments worked throughout the hours of peak 

flooding to keep bridges across the South Platte 

free of floating debris (The Denver Post, May 

7, 1973). Their actions probably saved many 

bridges from damage or destruction and diminished the severity of flooding along the banks. 

West of the city, scour was severe on such 

tributary streams as Coal Creek, Ralston Creek, 

Big Dry Creek, Leyden Creek, Van Bibber 

Creek, Lena Gulch, Mcintyre Gulch, Weir Gulch, 

Mount Vernon Creek, Bear Creek, Turkey 

Creek, North Turkey Creek, Deer Creek, and 

Massey Draw (figs. 6, 7). Much of the damage 

caused by these streams resulted from scour, 

undermining, blockage of culverts, and consequent inundation. Massey Draw did extensive 

damage at Chatfield Dam, on the Jefferson 

County side, when it broke out of an artificial 

channel and badly scoured engineered slopes 

and embankments (Edward E. McGregor, written commun., 1973) . Damage at Chatfield Dam 

totaled many thousands of dollars. 

8 

Roads, embankments, and bridges in the 

mountains were badly damaged by scour, primarily by overtopping and undercutting at 

places where channels were constricted by road 

embankments. Scour of this sort along Turkey 

Creek, North Turkey Creek, and Deer Creek 

caused the largest losses in Jefferson County. 

To the south, in Douglas County, scour damage was extensive at West Creek, West Plum 

Creek, Happy Canyon Creek, Sellers Gulch 

south of Castle Rock, Cherry Creek, West 

Cherry Creek, Willow Creek at State Highway 

470, Indian Creek, and several other small 

gulches (John 0. Maberry, written commun., 

1973) . Specifically, the following scour effects 

were noted by Maberry: 

West Creek damaged and closed State Highway 67 between Deckers and Woodland Park to 

the south; two small reservoirs failed in sequence, the upstream one first, by overtopping, 

thereby swamping the lower dam and creating 

a "wall" of water that destroyed much of the 

highway and several mountain homes (fig. 8). 

West Plum Creek washed out bridges at Sedalia and at Jackson Creek Road. It washed out 

culverts, dips, and weirs for irrigation ditches, 
FIGURE 6.- Severe bank scour by Bear Creek at West Dartmouth Avenue and South Newland Street, May 9, 

1973. Denver Post photograph by Bill Wunsch. 

scoured its banks laterally in many places and, 

in overtopping its banks, caused sheet flooding 

that silted cultivated fields. 

Plum Creek itself scoured and destroyed 

bridge abutments at Titan Road (east from the 

Martin Marietta Corp., toward Louviers), at 

Sedalia, on Douglas County Road 20 west of 

Sedalia, and at Louviers. Near Titan Road 

about 13 acres of land was badly eroded (E. E. 

McGregor, written commun., 1973). Many 

ranches along Plum Creek were isolated when 

access roads were severed by scour (The Parker 

Press, May 10, 1973). Scour undercut and collapsed the center span of a railroad bridge at 

the Du Pont Company plant in Louviers. Happy 

Canyon Creek and its tributaries damaged culverts and caused rockfalls in the Dawson Formation. 

Abutments of the West Cherry Creek bridge 

above Franktown, according to Maberry, were 

9 

destroyed by scour. The east abutment of the 

main stem Cherry Creek bridge on West Parker 

Road (Douglas County Road 8) was badly 

scoured. Cherry Creek washed out the bridge 

on the Parker-Castle Rock shortcut road and 

deposited sediment over about 50-100 acres of 

sod farms on its flood plain. It eroded its banks 

slightly at Havana Street, about half a mile 

downstream from Ch~rry Creek Dam. 

County Line Road (Colorado Highway 470) 

was closed between South University Boulevard 

and Interstate 25 when Willow Creek washed 

out twin 2-foot-diameter culverts and about 50 

feet of roadway. Maberry noted that countless 

unnamed tributaries, normally dry washes, and 

shallow drains did some damage by scouring 

and rill erosion, even on nearly fiat ground. He 

also noted that much of the stream scour in 

Douglas County coincided with the outsides of 
FIGURE 7. - Severe scour by Mount Vernon Creek east of Red Rocks Park. Area where figure is standing to left 

of center was a vegetable garden before the storm. Photograph by Eugene R. Hampton, May 7, 1973. 

FIGURE 8.-Severe scour by West Creek between Deckers 

and Woodland Park. State Highway 67 and many 

mountain cabins were damaged or destroyed. Before 

the flood, road beside cabin in background joined 

Highway 67 in foreground. Photograph June 1973 by 

Brent N. Petrie, consultant on land and water resources. 

bends. Scour in such places was prevalent 

throughout the metropolitan area. 

Tributaries on the east side of Greater Denver in Adams and Arapahoe Counties did relatively little scouring; Cherry Creek below the 

dam was largely restrained. Toll Gate Creek 

parallel to Interstate 225 eroded its banks 

slightly between East 6th A venue and Fitzsimons Army Hospital, a distance of about 12 

blocks. Sand Creek, historically troublesome, 

scoured its banks and channel considerably and 

transported and deposited large quantities of 

sediment. At Brighton Boulevard it scoured the 

abutments of a bridge but without structurally 

damaging the bridge itself (Robert M. Lindvall, 

written commun., 1973). Scour in the form of 

sheet wash and minor gullying was widespread 

in denuded areas undergoing construction. 

10 

SEDIMENTATION 

At flood stage, nearly all drainage through the 

Greater Denver area was overloaded with sedi-
FIGURE 9.- South Platte River just west of Brighton, May 6, 1973. Silt and mud damaged hundreds of acres of 

cropland and pasture. Aerial view is northeast toward East 160th Avenue in middle distance. Denver Post 

photograph by Barry Staver. 

ment, and deposition occurred where and when 

flow velocity was slowed. Sedimentation was 

subordinate to other flood effects in Greater 

Denver in terms of damage to property, but it 

caused local hardship to many people. Overbank 

flooding was the chief cause of sedimentation 

along most major streams, even while they were 

still scouring their channels. Scores of acres of 

flooded ground along the South Platte, including much cropland, received sediment from 

overbank flooding. North of Commerce City the 

South Platte River was out of its banks in a 

strip of land one-half to nearly 1 mile across 

(fig. 9). At Chatfield Dam, 60 acres was inundated. These areas were coated with mud when 

the water disappeared. Downstream, at Platteville, about 30 miles north of Denver, the mud 

reportedly was 3 feet deep and caused severe 

damage to pastures and cropland. 

Sheet flooding resulted when temporary rivulets spread out fanlike at the mouths of small 

11 

ravines or gullies. Much sediment was deposited 

on roads and streets. Some of these deposits 

graded into mudflows. 

Many tributaries without well-defined flood 

plains deposited large quantities of sediment 

when they were ponded by obstructed bridges 

or culverts. Obviously, these problems would 

not have arisen had the channels remained clear 

(fig. 10). 

MASS WAST AGE 

"Mass wastage" is a general term for the 

processes by which rock or earth material is 

transported en masse downslope. It includes 

landsliding (fig. 11) but excludes sediment 

transport by streams. Gravity is the chief transporting agent. 

Many small landslides, perhaps hundreds of 

them, were triggered in the western hilly part 

of the Greater Denver area by the storm of 

May 5-6. The moderate but steady precipitation 

saturated slide-prone areas, led to renewed 
FIGURE 10.- Overbank sediments deposited along Mcintyre Gulch at Holland Street in Lakewood, when culvert 

under street, behind observer, was unable to accommodate flood crest. Similar blockages caused flooding and 

sedimentation in many other places in Greater Denver area. 

FIGURE 11.- Form and nomenclature of a landslide 

(Varn ·s, 1958, pl. 1) . 

movement of many old landslides, and caused 

new landslides where none had existed previously. 

The landslides that ensued included slumps, 

earthflows, mudflows, debris slides and debris 

12 

flows, and rockfalls (in the nomenclature of 

Varnes, 1968, pl. I). Transitional forms were 

abundant, and the distinction between types 

was often arbitrary- the difference between a 

simple flood of muddy water and a true mudflow, for example, is largely a matter of the 

proportion of water to sediment. In most classifications, the so-called "mudslides" reported by 

the news media are highly fluid mudflows or 

debris flows. The term "flow" is more appropriate than the term "slide" because the mode of 

movement is essentially flowage rather than 

sliding. Similarly, mudflows grade into earthflows, and earthflows grade into slumps. 

Landslides occurred when the frictional 

forces that tend to hold a slope in place were 

exceeded by the gravitational forces that tend 

to cause it to move or fail. These forces can be 

expressed as a safety factor, s, which, in the 

simplest terms, is the total shear resistance, r, of 
the slope divided by the total shear force exerted, f. Thus, s=r If, and failure occurred when 

the ratio fell below 1.0-that is, when shear 

force exceeded shear resistance. Moisture, which 

reduces r, was (and is) the chief cause of failure, although many other factors generally contributed to the failure. The addition of moisture 

to marginally stable slopes on May 5-6 reduced 

the safety factor to 1.0 or less by (1) weakening the cementing bonds between soil and rock 

particles and, hence, reducing the internal shear 

resistance of the slopes, (2) adding weight to 

the potential slide mass, and (3) increasing the 

pore-water pressure in the interstices of the 

rock or soil. The effect of increased pore-water 

pressure was to "float" or suspend soil or rock 

grains relative to one another, thereby drastically reducing the shear strength of the mass 

and precipitating failure. 

Still another effect of adding moisture to the 

ground on May 5-6 was related to the behavior 

of soils that contain plastic clays having high 

swell-shrink ratios. Such clays, often called 

"bentonite," are common soil constituents in 

many parts of Greater Denver. They contain 

large proportions of certain clay minerals, such 

as montmorillonite, which have the property of 

greatly increasing their volume by the adsorption of water, or of shrinking with the loss of 

water. The adsorption of water not only changes 

A B 

the volume of the soil but, at the same time, 

adds weight and reduces shear strength which 

reduce the safety factor and lead to slope failure. 

SLUMPS AND EARTHFLOWS 

Slumps and earthflows were among the more 

prevalent kinds of landslides (fig. 12). Many 

existed in the western part of Greater Denver 

before the May 5-6 storm, many of these were 

further activated by the storm, and many new 

ones appeared during or after the storm. In 

the Greater Denver area sloping ground that is 

underlain by the Lykins, Morrison, Benton, 

Pierre, Laramie, or Denver Formation is more 

prone to landsliding than is other ground, because of the high proportion of plastic clay in 

these formations. Landslides occurred, however, 

even on the Precambrian terrane back in the 

mountains. 

A slump moves as a coherent block by displacement along a curved shear surface. The 

block rotates and slides about a horizontal axis 

on its center of gravity. Motion is arrested 

when the rebalancing of weight or an increase 

in friction returns the safety factor to more 

than 1.0. Because of their rotational habit, 

slumps tilt backward at their heads and bulge 

outward at their toes, and even slight movement 

is disruptive to a superincumbent structure. Most 

slumps in the Greater Denver area were comc D 

FIGURE 12.- Landslide types common in the western part of the Greater Denver area. From left to right: A, 

Rockfall moves mostly by free fall, bounding, and rolling ; B, slump by rotational slippage on concave-upward shear surfaces; C, debris slide by complex internal adjustments of highly deformed, sheared slide mass; 

D, earth flow by displacements and velocities similar to those of viscous fluids (Varnes, 1958, pl. 1). Illustrations by Natalie J. Miller, from Nilsen (1972). 

13 
FIGURE 13. - Debris-mudflow blocking Hogback Road about 1 mile north of Morrison on west side of Dakota hogback. Photograph by Eugene R. Hampton, May 7, 1973. 

pound in that they failed along multiple slip 

surfaces. Many of them, moreover, passed downslope into earthflows where the material tended 

to break up and disintegrate from wetting and 

flowage. This is the material that moved out 

onto the highways during the storm. 

Many small slumps and earthflows appeared 

along the outcrop of the Morrison Formation on 

the west side of the Dakota hogback, particularly at roadcuts where the natural slope had 

been oversteepened. Most of these small landslides were very wet and soupy, and they passed 

downslope into debris-mudflows (fig. 13). In 

some places removal of material from the roadways during cleanup operations only caused 

more material to flow into place. Arresting of 

motion in such places is possible only when the 

entire mass is removed or when the material 

finally dries out enough for flowage to stop. 

The flanks of both North and South Table 

14 

Mountain have had a long history of landsliding (Van Horn, 1954, 1972; Gardner and others, 1971; Simpson, 1973). West 32d Avenue 

was closed temporarily when many new slumps 

appeared on the north flank of South Table 

Mountain after the May 5-6 rains. Some older 

slumps were reactivated or accelerated, including the large landslide just south of Rolling 

Hills Country Club. Two long-active landslides 

above Clear Creek, one at West 32d A venue and 

one at West 44th Avenue (old Colorado Highway 58) were both in motion before the rains 

started (fig. 14) . Their prior activity had been 

promoted by the prolonged wet weather earlier 

in the season. Both showed evidence of increased 

movement after the May 5- 6 storm. 

Because of the heavy moisture take-up by the 

Highway 58 slide, the damage potential of continued movement had been very large, involving 

an imminent threat to new Colorado Highway 
FIGURE 14. - Landslide in Denver Formation on old Colorado Highway 58, one-half mile east of Golden at foot 

of North Table Mountain. This slide has been intermittently active for many years and has been a continuing problem for highway and railroad maintenance people. Present activity was aggravated by the May 5-6 

rains. 

58, continuing damage to West 44th Avenue, 

continuing damage to the Colorado and Southern Railroad tracks, potential disruption of the 

Farmers Highline Canal, and a serious threat 

to the Coors Co. sewage-disposal plant. The 

Colorado Highway Department, therefore, has 

taken steps to rectify the conditions that led to 

slide movements in. the past. 

Many small slumps, earthflows, and mudflows appeared in backfilled areas along Interstate 70 in the mountains (fig. 15). Most of 

these were superficial failures involving only 

topsoil or dressing on sloping rock cuts. Mudflows appeared mostly on steep slopes where 

grass seeded the previous summer and fall had 

not yet established a protective turf. Even a 

good cover of turf, however, will not prevent 

slumping- in contrast with mudflowage- if 

the subsoil is saturated. The effects of the above 

15 

FIGURE 15.- Small debris slide on eastbound exit ramp 

of Interstate 70 at Genessee Mountain. Material is 

loam slope dressing and colluvium. 
failures to date have not been hazardous, but 

they will present continuing maintenance problems unless arrested, and they could, perhaps, 

lead to some blockage of traffic lanes. 

Northwest of Arvada, old slumps and earthflows are abundant around the edges of Rocky 

Flats. The Laramie Formation and the Pierre 

Shale are host rocks for most of these slides. A 

few of these were reactivated by the May 5-6 

rains, and many new ones appeared for the first 

time (fig. 16). Most of these slides are along 

roadcuts, where marginally stable slopes had 

been oversteepened by highway excavations. 

Other small slides were triggered near the bottoms of gullies where bank scour set off slumps 

or earthfalls. A detailed survey probably would 

disclose scores of small failures of this sort. 

East of Rocky Flats, two small landslides 

partly blocked the southbound lane of Colorado 

Highway 121, about three-fourths mile and 1 

mile south of the Broomfield interchange 

(fig. 17). This area is underlain by highly expansive soil, if the bumps and waviness in the 

pavement are any indication. The southern slide 

had begun to fail several weeks before the May 

5-6 storm when cracking and minor bulging 

first appeared, but the major movement was 

triggered by the May 5-6 rain. Movement was 

continuing in both slides at a diminished rate 

during the last week of May. 

FIGURE 16.- Small slump in Laramie Formation on 

Boulder County road 2 miles west of Jefferson County 

Airport. Oversteepened slope and heavy rains triggered failure. Crown of slide is about 20 feet above 

roadway. Photographed on May 8, 1973. 

16 

FIGURE 17.- Slump-earthflow on Colorado Highway 

121 about three-fourths mile south of Broomfield interchange. Toe of landslide partly blocked southbound 

lane but was promptly cut back by Highway Department. Photographed on May 8, 1973. 

MUDFLOWS 

Small mudflows ran down both sides of the 

Dakota hogback west of Denver, especially between Interstate 70 and Morrison. They were 

abundant also on steep slopes in the foothills 

of Jefferson County - myriads of them scarred 

the new cuts of Interstate 70. 

In Platte Canyon at the Denver Water Board's 

intake structure 3 miles above the Kassler Filter Plant, a mudflow engulfed the caretaker's 

house, which had stood undamaged for about 

60 years (Quentin Hornback, oral commun., 

1973, relayed by Robert M. Lindvall). 

Debris-mudflows ran down several of the 

steep-sided buttes in the Plum Creek drainage 

in Douglas County (John 0. Maberry, written 

commun., 1973). Some of these were accompanied by rockfalls. 

In summary, small mudflows were common 

consequences of the storm in hilly or mountainous parts of the metropolitan area wherever 

sparsely vegetated hillslopes were underlain by 

shaly, clayey, or silty subsoils. Mudflows originated chiefly in the Morrison, Benton, Pierre, 

Denver, and Dawson Formations and in clayey 

or silty colluvium. They caused considerable 

inconvenience and some hazard where they 

flowed onto highways, but, in terms of total 

storm effects, their damage was minor. 
FIGURE 18.- Rockfall on eastbound lane of Interstate 70, 2 miles west of Bergen Park interchange (El Rancho). 

Failure was along joints (fractures) and foliation planes (layering) in Precambrian gneiss. Rockfall obstructed all of eastbound lane and median and part of westbound lane before cleanup began. Estimated weight 

of largest boulders exceeded 200 tons. Photographed on May 8, 1973. 

ROCKFALLS 

Rockfalls were triggered by the storm on the 

steeper hillsides and canyon walls west of Denver when rainwater and snowmelt percolating 

into cracks loosened rock fragments and sent 

them plummeting down the slopes. Loose mantle rock behaved similarly. Rockfalls were abundant in the canyons as far west as Berthoud 

Pass along U.S. Highways 6, 40, and 285, Interstate 70, and Colorado Highway 7 4. Most of 

these were quickly removed by highway maintenance crews. 

By far the largest single rockfall collapsed 

onto Interstate 70 about 2 miles west of Bergen 

Park interchange, near El Rancho (fig. 18), 

completely blocking the eastbound lane. Some 

rock bounded across the median and into the 

westbound lane. Failure along steeply dipping 

foliation planes (layering) and joints (frac17 

tures) involved thousands of tons of rock, including giant boulders weighing hundreds of 

tons each that required drilling and blasting 

before they could be removed. The hillside above 

the fall was left in a precarious state, also, and 

much loose rock had to be drilled and blasted 

before cleanup work could start on the rockfall 

itself. 

South of the metropolitan area in suburban 

Douglas County, rockfalls collapsed down the 

flanks of several steep-sided buttes south and 

west of Plum Creek, particularly Dawson Butte, 

Raspberry Mountain, and Bald Mountain (John 

0. Maberry, written commun., 1973). Rockfalls 

at these places resulted when failure of the soft 

claystones and sandstones in the Dawson Formation removed support from the overlying 

cap rock. 
TOWARD COPING WITH FUTURE STORMS 

Greater Denver's history of intense rainstorms and destructive flooding extends back 

into pioneer days and even into Indian legend. 

(See Follansbee and Sawyer, 1948, for an excellent general reference, and Matthai, 1969.) 

Floods undoubtedly will occur in the future just 

as they have in the past. In fact, the South 

Platte was out of its banks again on May 24, 

1973, and flash-flooding tributaries on June 12, 

1973, took three lives. As urbanization spreads 

over the Colorado Piedmont, the frequency and 

intensity of urban flooding are likely to increase. 

Measures can be taken, nevertheless, to forestall problems, and the initial cost of prevention 

in the areas of new construction can be more 

than recovered in the long-term savings from 

minimized storm damage. In older areas, where 

the problem is more complex, rectification is 

more difficult and much more costly. 

Geologic processes triggered by the May 5-6 

storm were intensified in places where the natural regimen had been altered by man. Inasmuch 

as such alterations are inevitable in any rapidly 

growing urban area, careful planning to ensure 

compatability with natural processes is essential if destructive side effects of heavy storms 

are to be minimized. 

Some common land-development practices in 

the Greater Denver area that tended to accelerate geologic processes and aggravate the intensity of storm effects were (1) channeling 

drainage into concentrated systems that are 

incapable of accommodating peak storm runoffs, 

(2) inhibiting infiltration of moisture by reducing permeability and speeding runoff, (3) blocking or constricting natural drainages by dikes, 

bridges, culverts, and landfills, and ( 4) oversteepening natural slopes by undercutting or 

by filling at angles steeper than those that 

commonly persist in nature, particularly along 

rights-of-way for highways but also in housing 

developments in hilly areas. The effects of some 

of these practices seem to be self-evident, and 

to recapitulate them may be to restate obvious 

generalities, but there is some value in viewing 

diverse land-development practices in a perspective that relates one consequence to another. 

All these practices tend to compound the overall 

effects of a storm by reinforcing one another at 

the critical time of maximum storm intensity. 

18 

Channeling drainage into systems that are unable to accommodate peak runoffs, for example, 

is a common consequence of inhibited infiltration, which, in turn, often results from the 

multitudinous land modifications associated with 

urbanization. 

Another lesson that should now be clear is 

that gully bypasses, such as flumes, conduits, 

or siphons, are needed to prevent unwanted 

storm drainage from entering and overwhelming canals and ditches. 

Inhibited infiltration, particularly because of 

impervious surfaces, such as roofs, driveways, 

sidewalks, streets and especially parking lots, 

increased storm runoff enormously. Artificial 

retention systems can be designed, on the other 

hand, to reduce runoff rates to acceptable levels. 

Large flat-topped roofs can be designed to provide temporary storage for slow release or 

evaporation. Downspouts from houses and commercial buildings can be directed onto lawns or 

other pervious areas where infiltration is possible and desirable. In some places, runoff can 

be recharged directly to the ground water by 

means of French drains, dry wells, or similar 

infiltration systems. Infiltration obviously should 

be avoided in potentially unstable slope areas 

where landsliding might be initiated or in areas 

where moisture might gain access to high swellshrink clays beneath footings or poured slabs. 

In some places ponds can be designed to catch 

and hold excess runoff. When suitably landscaped, such ponds are assets that increase the 

value of adjoining real estate. 

Heavy earthmoving equipment has made possible the economic development of large tracts of 

land. Such construction practices in the Greater 

Denver area, however, commonly denude large 

acreages of land for extended periods of time 

prior to construction and, during heavy rainstorms, greatly increase the vulnerability of the 

land to sheet wash, gullying, scour, mudflowage, 

and sedimentation (fig. 19). These costly storm 

effects can be reduced if, following the lead of 

the highway builders, provisions are made for 

rapid, even temporary, revegetation with fastgrowing grasses and herbs to reestablish protective ground covers, reduce erosion, and retard 

runoff. Better yet, careful analysis of the landscape at the planning stage can often minimize 

the initial alteration of the natural land surface 
- -----

FIGURE 19.- Gullying on a steep hillside previously denuded of vegetation and topsoil. 

and prevent unforeseen geologic complications. 

Blockage of natural drainageways was one 

of the principal causes of flood damage in the 

Greater Denver area. Many bridges and culverts 

were simply unable to accommodate the increased runoff; many were blocked with trash 

or sediment. In the urban environment, natural 

drainageways that seem unsuitable for one purpose or undesirable from one point of view may 

enhance the value of an area for something 

else. Most natural landscape features have the 

potential for being either liabilities or assets. 

During a major storm, an urbanized or industrialized flood plain is likely to be a liability, 

not only because of direct flood damage to facilities on the flood plain but also because of the 

obstructions that such facilities present to the 

free passage of the water. Such facilities, in 

other words, can actually intensify the effects 

of flooding. But a flood plain that is dedicated 

as parkland, open space, or wildlife habitat in 

19 

an otherwise crowded city is nearly immune to 

flood damage and is likely to become a community asset that increases in value with time. 

Overland Park on the South Platte flood plain 

is a good example. The numerous ravines and 

gullies that drain the Greater Denver area 

ought to be natural assets that enhance the 

quality of urban living, but many of them are 

financial liabilities to the community and some, 

regrettably, are festering eyesores. Protecting 

natural drainageways should be a prime consideration of long-range planning. Existing 

structures that tend to obstruct drainage might 

well be phased out of use. Unobstructed drainageways not only afford insurance against storm 

damage from high runoff but they provide some 

of the open space that is fast disappearing from 

the urban scene. 

Damaging floods are not restricted to streams 

that have broad flood plains. Indeed, an urban 

drainageway need not have any flood plain at 
all to generate a damaging flood. Even a small, 

normally dry watercourse is capable of inflicting damage, especially if its path is obstructed 

by manmade structures. One must remember 

that a ravine is the product of erosion by running water, that streams erode most effectively 

during occasional flood stages which greatly 

exceed normal flow, and that the lack of appreciable runoff in an innocuous-looking ravine does 

not imply that great volumes of water may not 

occupy the watercourse during a heavy storm. 

Oversteepened slopes contribute greatly to 

storm damage. By far, the majority of slope 

failures that we observed immediately after the 

May 5-6 storm-slumps, earthflows, mudflows, 

and rockfalls- were consequences of manmade 

alterations. They occurred where slopes had 

been oversteepened, either by cutting or by filling, beyond the bearing capacity of the material 

in the slopes. If similar failures are to be prevented in the future, careful stability analyses 

must precede slope modifications. Expert professional judgment is needed to evaluate such 

slope problems in hilly parts of Greater Denver 

before construction work is started. Sound engineering practices must go hand in hand with 

cutting or filling operations in hillside situations. 

Loose fills dumped into gullies or onto hillsides at the angle of repose of dry material are 

foredoomed to eventual failure; mute testimony 

was provided by some such failures after the 

May 5-6 storm. As a word of caution, slope 

modifications should be held to a minimum in 

geologic settings where the risk of slope failure 

is high. In general, the risk is highest in areas 

where bedrock or overburden contains a high 

percentage of plastic shale or clay, especially 

clay having high swell-shrink properties, and 

areas where appreciable moisture is likely to 

enter the ground either naturally or artificially. 

Much hilly terrain in the western part of the 

Greater Denver area has a high risk potential 

for slope failure if modified by cutting or filling. 

Much of this terrain, however, also has natural 

attributes that would be highly desirable in 

scenic easements, green belts, or natural parks 

and that can contribute, therefore, to an increased quality of living in the area. With foresight and planning, potential liabilities to the 

community can become genuine assets. 

REFERENCES CITED 

Ducret, G. L., Jr., and Hansen, W. R., 1973, Storm of 

May 5-6, 1973, in the Denver Metro Area- Frequency and Effect: Urban Drainage and Flood 

Control District, Denver, Colo., 40 p., 6 figs., 

5 tables. 

Follansbee, Robert, and Sawyer, L. R., 1948, Floods in 

Colorado: U.S. Geol. Survey Water-Supply Paper 

997, 151 p. 

Gardner, M. E., Simpson, H. E., and Hart, S. S., 1971, 

Preliminary engineering geologic map of the Golden 

quadrangle, Jefferson County, Colorado: U.S. Geol. 

Survey Misc. Field Studies Map MF-308. 

Matthai, H. F., 1969, Floods of June 1965 in South 

Platte River basin, Colorado: U.S. Geol. Survey 

Water-Supply Paper 1950-B, p. B1-B64. 

Nilsen, T. H., 1972, Preliminary photointerpretation 

map of landslide and other surficial deposits of the 

Mt. Hamilton quadrangle and parts of the Mt. 

Boardman and San Jose quadrangles, Alameda and 

Santa Clara Counties, California: U.S. Geol. Survey Misc. Field Studies Map MF-339. 

Simpson, H. E., 1973, Map showing landslides in the 

Golden quadrangle, Jefferson County, Colorado: 

U.S. Geol. Survey Misc. Geol. Inv. Map I-761B. 

Van Horn, Richard, 1954, Landslides near Golden, Colorado: Engineers Bull., v. 38, no. 12, p. 6-15. 

___ 1972, Surficial and bedrock geologic map of the 

Golden quadrangle, Jefferson County, Colorado: 

U.S. Geol. Survey Misc. Geol. Inv. Map I-761A. 

Varnes, D. J., 1958, Landslide types and processes, in 

Eckel, E. B., ed., Landslides and engineering practice: N atl. A cad. Sci.-N atl. Research Council Pub. 

544, Highway Research Board Spec. Rept. 29, 

p. 20-47. 

*u.s. GOVERNMENT PRINTING OFFICE: 1973 0-543-579/56 

20