C153379 Feasibility Study

• Contract/PO #: C153379
• Contractor Name: Brook Forest Water District
• Contract Type: Loan
• Water District: 9
• County: Jefferson
• Bill Number: SB 80-67
• Loan Projects - Doc Type: Feasibility Study

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streams washed tremendous volumes of sand and gravel onto the plains. During

the warm, wet cycles, weathering and soil formation occurred near the top of

the newly-deposited sand and gravel deposits. High winds during several parts

of the Pleistocene deposited loess (aeolian silt) over most of the earlier

deposits.

The end of the Pleistocene saw the retreat of the glaciers, which

continues to the present. Erosion and deposition by streams, fed by spring

runoff of melted snow, and coqtinued erosion and deposition of wind-blown sand

and silt have characterized the most recent 10,000 years.

3. Bedrock Geology

The calcareous mud deposited during the long stand of the Cretaceous

inland sea (Chapter III, B.2) formed the Pierre Shale (Table III-i). The

Pierre consists of 5800 ft of silty shale, siltstone and thin sandstone

and limestone beds in the Hardin area (Gardner, 1967). The proposed dam site

is directly underlain by the upper transition zone of the Pierre, a 2700 ft

thick unit of sandy claystone, soft shaly sandstone, massive friable sand-

stone and large calcareous sandstone concretions (Scott and Cobban, 1965).

The sandbar and beach deposits laid down over the calcareous mud formed

the Fox Hills Sandstone, a light-brown, thinly bedded to massive sandstone

with intertonguing lenses of Pierre-like sandy shale (Gardner, 1967). Due to

the transitional nature of the contact between the Pierre and Fox Hills, no

distinct contact and no exact thickness have been determined in the Hardin

area. However, the sandstones of the Fox Hills definitely outcrop along the

Empire Canal in the south or right abutment of the proposed dam. The thick-

ness of the Fox Hills is probably 50 to 100 ft in this area.

The lagoon, delta and swamp deposits of the late Cretaceous became the

claystone, sandstone and coal beds of the Laramie Formation (Figure III-I).

The Cretaceous and early Tertiary terrestrial stream, fan and mudflow deposits

formed the Denver-Dawson Formation in the Denver Basin. The later Tertiary

continental lake, stream and fan deposits formed the White River Group and the

Arikaree and Ogallala Formations on the eastern plains. Although all of these