In addition to the cultural record, a geologic history
is represented at the Landmark. The different sediments and buired
soils indicate the local environment at various periods. The soils
indicate numerous periods when the landscape was stable (no erosion
or accumulation of sediment occurred). From these deposits, nearly
175 radiocarbon dates are available.
The bedrock of Lubbock Lake is the Blanco Formation.
It is composed of an extensive deposit of lake sediments about 2
million years old. Above the Blanco Formation is the Blackwater
Draw Formation, a sheet of wind-deposited sediment that covers most
of the region. This deposit slowly accumulated between 1 million
and 50,000 years ago. The Dune, in the northeastern section of Lubbock
Lake, contains sediments and buried soils from at least 36,000 years
ago. Yellowhouse Draw developed by 20,000 years ago, cutting through
the Blackwater Draw Formation and into the Blanco Formation. By
about 12,000 years before the present (B.P.), the draw had cut a
meander (horseshoe bend) about 15 meters (49 feet) deep in the area
of the Landmark.
Evidence points to a drying trend occurring at Lubbock
Lake over the last 11,000 years. The geologic record begins with
stream deposits, followed by lake sedimentation, and culminating
between 6,500 and 4,500 years ago with the deposit of windblown
sediments during a period of severe drought. After 4,500 years ago,
the climate was much as it is now with minor alterations in the
past 2,000 years.