1987-12-01_PERMIT FILE - C1981017 ‎(289)‎

• Permit No: C1981017
• IBM Index Class Name: PERMIT FILE
• Doc Date: 12/1/1987
• Doc Name: Geotechnical Investigations Mine Portal Benches and Haul Roads
• Section_Exhibit Name: Chapter V Appendix V-E-II
• Media Type: D
• Archive: No

Dacite porphyries appear densely fractured in several
outcrops along the roads; otherwise , they are very hard and
resistant rocks.
Much of the area is covered by Quaternary deposits such as
colluvial soils, alluvial deposits and landslides. Colluvial
soils cover many slopes of the Basin; they are very thin or
absent on steep slopes , but their thickness increases
considerably in areas of moderate slopes. They are usually
clayey-silty soils, with a frequent admixture of cobbles and
boulders of Mesaverde sandstones, dacite porphyry or basaltic
rocks.
Alluvial desposits are limited to narrow strips along the
larger creeks in the area. They have a typical character of
high mountain sediments deposited during flash-floods and
periods of intensive spring melt. They contain a large
percentage of basaltic gravel and boulders.
Landslides of a large extent are relatively infrequent in
the Coal Basin area. Several large landslides have been
identified in the Basin during our work for different projects;
it appears that no significant landslide can be found within
the area of the haul roads and mine benches. Minor slides and
unstable slopes can be found locally; they are of limited
importance for the reclamation of the road system and mine
benches.
As a result of the topographic conditions of the area, its
high altitude, low resistance of Mancos Shale to erosion, and
intensive erosional process, one more soil type can be found;
it can be classified as outwash deposits. Such soil frequently
covers flat parts of the valleys ; the cover is sometimes of
considerable thickness and usually contains large boulders of
Mesaverde sandstones. As most of these deposits have been
derived from Mancos Shale , they contain a significant
percentage of clay.
The morphology of the Coal Basin has been very much in-
fluenced by the geologic structure. The Coal Basin has a dis-
tinct anticline structure with the anticline axis being close
to parallel with the valley axis. Both anticline flanks dip
gently ( 5 to 25 degrees) , to the northeast on the east valley
side , and to the southwest on the west valley side where all
Coal Basin mines have been developed.
Such geologic setting is quite unusual in Colorado ; as a
result of this structure, the formations dip into the mountain
on both valley sides. Valley sides with such a formation dip
are usually stabler than the valleys with formations dipping
into the valley. The Coal Basin structure is also favorable
from the hydrological point of view; it can be expected that
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GEO-WMRO CONSULTING,INC.
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