Time:
Early Archaic - 8,500 to 6,400 years ago |
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Sediments:
Mild winters with periods of freezing temperatures persisted though
summers were warming. The prairie habitat became dominant in the
draw environment, indicating a decrease in available moisture
and humidity levels with periodic summer droughts. The valley
floor was a wet meadow marshlands that graded into an open prairie.
A soil layer named Firstview Soil developed from about 8,500 to
6,300 years ago with high organic content in the marshy areas
and less so in other areas. The soil formed in a boggy area with
a water table close to or occasionally at the surface but without
expanses of water of any depth.
Plants:
A
freshwater marsh surrounded by bulrushes continued along the valley
floor. Gaura grew in the dry, sandy slope wash area. The local
environments reflect the continued warming and drying conditions.
The faunal community is a modern one, indicating a decrease in
available moisture and humidity levels.
Time:
Middle Archaic - 6,400-4,500 years ago
Sediments:
During the earlier part of the Middle Archaic, the area suffered
a harsh drought that lasted for nearly 1,000 years. Effective
moisture decreased with little to no rainfall and poor surface
water leading to extremely dry and dusty conditions. A hard-water,
brackish marsh existed in the draw with the water table at or
just below the surface. The soil layer named Yellowhouse Soil
developed in these deposits. Areas of sandy soil grassland dominated
the prairie.
Plants:
The marsh supported bulrushes and water lilies (Nymphaeaceae).
Areas of sandy soil grassland still dominated the prairie, but
forbs and herbaceous vegetation were present as well, indicated
by the presence of pronghorn antelope, a browsing animal. Abnormalities
in the teeth of bison found during this period indicate poor range
conditions due to excess grit on the vegetation from the large
amounts of dust in the air at that time and drifting sediments
indicate a great reduction in vegetation cover.
Sediments:
A short-term break (5,500-5,000 years ago) from the Middle Holocene
drought, is found only along the valley floor. It contains sandy
deposits from an intermittent stream intermingled with clayey
marsh deposits. This indicates that precipitation increased and
the dust stopped blowing.
Plants:
A small freshwater stream flowed in the valley axis and supported
water lilies. The vegetation cover stabilized and sod forming
grasses returned. Although not as dry as the previous years, the
area still was dry and warm (semiarid) with a desert grassland.
Sediments:
Sediment from the end of the Middle Archaic is primarily a wind
blown sandy deposit interpreted as dust and drought returning
to the region. Nevertheless, fresh water was available at the
surface as some marsh deposits also occur.
Plants:
By the end of the Middle Archaic surface water again decreased
greatly. Open prairie with dry prairie to desert conditions returned,
indicating a second period of blowing dust, reduction in vegetation
cover, and decreasing effective moisture.
Time:
Late Archaic - 4,500-2,000 years ago
Sediment: During the Late Archaic,
the marshland returned in the valley. Blowing dust ceased, indicating
a return to a stable vegetation cover. Soil named the Lubbock
Lake Soil began forming approximately 4,500 years ago. This is
the time when the modern regional climate emerged, with a return
of more available moisture from precipitation and surface waters,
along with the modern short-grass prairie.
Plants:
By 4,500 years ago, the modern regional climate emerged, with
a return of more available moisture from precipitation and surface
waters, and the modern short-grass prairie. During the Late Archaic
(4,500-2,000 B.P.), the marshland returned in the valley. Blowing
dust ceased, indicating a return to a stable vegetation cover.
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