Sometimes the border of the Chihuanhuan Desert reaches into this part of Texas and brings with it intense desertification. From 8,000 to 5,000 years ago was the time of the Mega Drought, officially known as the Mid-Holocene Climatic Optimum among paleoclimatologists and to archeologists as the altithermal and the early Archaic period. One explanation is that a wobble in the Milankovitch Cycle caused increased solar radtiation which drove up the temperature on the Great Plains by 7 degrees Fahrenheit. This heating pulled the Inter-Tropical Convergence Zone, the rain belt, to the north and supressed El Nino activity for a very long time. Below the equator where it was cooler and wetter, the Sahara Desert was green, it was springtime in Mesopotamia. But in Texas is was scorching , the Bosque River dried up and the people moved away. Almost. Droughts are associated with significant erosion and sedimentation because the sudden hurricane-related rain event will not be restrained by thick grasses, so many archeological sites were scoured away and buried.Cactus and some grasses (like Texas grama) used wide-ranging shallow roots to capitalize on rare rainfall and then store the moisture. Historians/archeologists have been slow to piece together information to explain the sequence of events during the altithermal. Ice cores are usually loaded with information about world climate history, but during this period the arctic ice was melting. Pollen studies in Texas show that post oaks and even pecan trees were holding on. Human occupation along the Bosque River is lightly indicated by an Early Archaic split-stemmed dart tradition represented locally by the Gower type. These people introduced the use of the metate, a sandstone grinding slab, hot-rock baking, and a broader adaption on plants – especially prickly pear (Opuntia).

Dan Young, Unpublished Manuscript, 2022