The preceding part of this chapter mentions many ways in which man’s
destiny in Colorado has been shaped by geologic factors. Early
Coloradoans settled near gold and silver placers, later ones near mines
that produced ores of other metals, or in the towns that sprang up
around the mills and smelters that processed these ores. Our present
distribution of population is partly a heritage from these first
settlements, partly a result of later discoveries of oil, gas, and
radioactive minerals, and partly a response to the state’s extreme
topographic variation, which controls and delineates agricultural areas
and transportation routes.
In recent years, man has begun to appreciate the fact that he may
benefit in other ways from knowledge about geology. A new geology has
developed—_environmental geology_—which may be defined as the total of
all geological conditions and influences affecting the life and
development of man.
Environmental geology is a broad science, concerned not only with the
location of cities and towns, but with the uses people make of the land
and its economic products, and with the relationship between the
geological character of the land and the present and future location of
roads, dams, bridges, factories, homes, recreation facilities, sanitary
land fills, and even sewage plants.
Two aspects of environmental geology which are particularly pertinent to
Colorado’s residents are discussed below.
_Landslides_ and slumping rock or earth are a frequent menace to
Colorado’s development in the Mountain Province. Often activated by
heavy rains or deep manmade cuts, they can cause—and _have_ caused—much
damage to roads, buildings, and other works of man.
The flanks of North and South Table Mountains, near Golden, are mantled
by thick landslide debris; intermittent movement of the individual
slides has repeatedly affected the railroad, irrigation ditches, and
roads. As many as six different slides have moved within a single year.
In one slide area, asphalt road material is estimated to be thirteen
feet thick; successive layers of pavement have been laid one on top of
another to keep the street up to grade.
Landslides and landslide-prone areas may not be obvious to the untrained
eye. Each year buildings and roads are constructed on unsuitable rock
and soil foundations, in places where some degree of land slip is almost
inevitable. Building in such areas is risky, but sometimes worth the
risk; if condition are less than ideal, risks can be reduced by
specialized types of construction.
_Floods_ are a perennial threat to much of the state, because of the
high relief of the drainage basins and the torrential nature of the
spring and summer rainfall. Their damaging effects were realized early
in Colorado’s history, when canyons were used as highways and railroad
routes.
Colorado’s most expensive flood was probably the flood in the South
Platte River basin south of Denver in 1965, which caused $508,000,000
worth of damage and drowned six people. The losses can be attributed to
man’s failure to realize the significance of the South Platte drainage
routes and flood plains. Homes, shopping centers, and many other
buildings occupied—and still occupy, as of 1971—land that has been
intermittently flooded for many years. The following description of this
flood, by H. F. Matthai of the U. S. Geological Survey, may help to
convey some warning to residents or potential residents of the South
Platte valley and other river valleys in Colorado:
“The morning of June 16 was most pleasant, but conditions changed
rapidly shortly before noon. A tornado touched ground 15 miles south
southeast of Denver about 1 p.m. Within the next hour, another unroofed
30 homes in the little town of Palmer Lake, 40 miles south of Denver.
About 2 p.m., a dense mass of clouds descended and concealed the top of
Dawson Butte, 7 miles southwest of Castle Rock; and the little light
remaining faded until it was dark black and frightening, according to
some people. A nearby rancher’s wife described the intense quiet as
awesome, but the calm did not last very long.
“The deluge began, not only near Dawson Butte, but also at Raspberry
Mountain, 6 miles to the south, near Larkspur. The rain came down harder
than any rain the local residents had ever seen, and the temperature
dropped rapidly until it was cold. The quiet was shattered by the
terrible roar of wind, rain, and rushing water. Then the thudding of
huge boulders, the snapping and tearing of trees, and the grinding of
cobbles and gravel increased the tumult. The small natural channels on
the steep slopes could not carry the runoff; so water took shortcuts,
following the line of least resistance. Creeks overflowed, roads became
rivers, and fields became lakes—all in a matter of minutes.
“The flow from glutted ravines and from fields and hillsides soon
reached East and West Plum Creeks. The combined flow in these creeks
have been described as awesome, fantastic, and unbelievable; yet none of
these superlatives seem adequate to describe what actually occurred.
Large waves, high velocities, crosscurrents, and eddies swept away
trees, houses, bridges, automobiles, heavy construction equipment, and
livestock. All sorts of debris and large volumes of sand and gravel were
torn from the banks and beds of the streams and were dumped, caught,
plastered, or buried along the channel and flood plains downstream. A
local resident stated, ‘The banks of the creek disappeared as if the
land was made of sugar.’
“The flood reached the South Platte River and the urban areas of
Littleton, Englewood, and Denver about 8 p.m. Here the rampaging waters
picked up house trailers, large butane storage tanks, lumber, and other
flotsam and smashed them against bridges and structures near the river.
Many of the partly plugged bridges could not withstand the added
pressure and washed out. Other bridges held, but they forced water over
approach fills, causing extensive erosion. The flood plains carried and
stored much of the flood water, which inundated many homes, businesses,
industries, railroad yards, highways, and streets.
“The flood peak passed through Denver during the night, and the
immediate crisis was over by morning; but those in the inundated areas
were faced with a Herculean task. The light of day revealed the nature
of the destruction—mud in every nook and cranny, soggy merchandise,
warped bowling alleys, drowned animals, the loss of irreplaceable
possessions, to name a few types. The colossal cleanup job, which would
take months, began.”
Hydrogeological studies by the U. S. Geological Survey and Corps of
Engineers give knowledgeable estimates of flood danger for different
populated areas of the state, and recommend that homes, roads, and other
structures be placed above likely flood levels.