FLOOD04800

• County: El Paso
• Community: Colorado Springs
• Stream Name: Cottonwood Creek
• Basin: Arkansas
• Title: Engineering Study of Cottonwood Creek Drainage Basin
• Date: 8/7/1979
• Prepared For: Colorado Springs
• Prepared By: Lincoln Devore
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Basin Geoloqy. Soils, and Water Table

Basin Geology of the Cottonwood
Creek basin is not complicated. Except for a few areas in the

incised Monument creek, the entire basin is underlain by members

of the Tertiary Dawson Formation. A small exposure of the Laramie

~ormation was noted in the southwest corner of the basin, low in

Monument Creek. Thjs is so small as to be unimportant from the

hydrologic point of view. The Front Range Fault is located west of

the site and far enough away that it has no structural control over

the basin.

The Dawson group is a rather erratic

formation from the standpoint of soils produced, In general, it is

a series of weakly cemented sandstones, most of which are Arkosic.

Some units of sandstones are relatively competent, do not erode

easily and tend to form cliffs, This can be seen at a number of

creek incisions and in the erosion pattern along the south basin

line. Most units of the sandstone are easily eroded and broken down

into their component soil types. Erosion in some of the formation

can take place very rapidly. Several wagon roads in the area which

existed prior to 1940 as roads, are now fairly deep gullies.

The basic sandstones of the formation

are composed of varying p~rcentages of sands, gravels, silts and

clay. The rate of erosion is generally controlled by the relative

percentage of these constituents at any given point. The formation

is also noted for containing large lenses of claystones. These

lenses are usually hard and in some cases, are quite sensitive to

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