PROJ00132

• Contract/PO #: FS0014X
• Contractor Name: Southern High Plains Ground Water Management District
• Contract Type: Loan
• Water District: 0
• County: Prowers
• Loan Projects - Doc Type: Feasibility Study

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Oklahoma and are rarely penetrated by water wells in Colorado. They are shown as the
basal unit in the cross-sections described in Section 9.0.

7.2.3 Dockum Group
The Dockum Group outcrops only in the deep canyons of Black Mesa in southwestern
Baca County and southeastern Las Animas County; at Two Buttes Reservoir; and in
limited exposures adjacent to the Cimarron River in southeastern Baca County. These
Triassic red beds are mostly interbedded red siltstones, shales and limestones with red
to buff, fine- to coarse-grained sandstones. The lithology of the group varies significantly
at each of these outcrops. The Dockum is correlative with the Lykins Formation to the
north in central Colorado. The Group is rarely penetrated completely by wells or
erosion, and is estimated to be between 300 and 570 feet thick in Baca County.

7.2.4. Jurassic Undifferentiated
Rocks of Jurassic age include the Entrada Sandstone and Morrison Formation. These
outcrop only in the canyons in the southwestern part of the Basin and adjacent to Two
Buttes and are undifferentiated in the cross-sections of this study. Both formations are
miS-sing in eastern Baca County where they were truncated prior to deposition of
Cretaceous rocks. The Entrada unconformably overlies the Dockum and ranges in
thickness from approximately 380 feet in the north near Two Buttes to non-existent in the
east where it pinches out on top of the Dockum. The Entrada. is predominantly gray to
buff, fine- to medium-grained sandstone. It is generally friable and forms rounded cliffs
where exposed.

The Morrison is composed of marl, siltstone, clay and shale with some interbedded
sandstone, limestone and conglomerate. The maroon, red, gray and green variegated
shales are distinct in outcrop, but can be confused with the underlying Dockum red beds
in drill cuttings. The Morrison is reported to range from 0 to 325 feet in thickness.

7.2.5. Cheyenne Sandstone
The Cheyenne Sandstone is considered as the lower member of the Purgatorie, with the
Kiowa Shale being the top member. The Cheyenne, Kiowa and Dakota are each clastic,
lower Cretaceous formations comprised of interbedded gray sandstone, siltstone and
shale. The Cheyenne and Dakota are predominately sandstone and the Kiowa
predominately shale; distinction of these units in drill cuttings can be difficult. As
described below, the discontinuity and heterogeneity of the Kiowa suggests that it is
largely a leaky interval between the water-bearing Dakota and Cheyenne units.

VII-2