Tecopa Mud Hills
The Tecopa Mud Hills, near Tecopa, California, form a stark badlands landscape shaped from ancient lake deposits. Sparse vegetation lines the margins, but the interior hills are largely barren, composed of crusted ash and pale sediment. These formations preserve the remnants of Lake Tecopa, which filled the basin during a wetter climatic period in the late Pliocene and early Pleistocene.
During this time, a moderately deep lake occupied the Tecopa Basin. As the lake expanded and contracted over thousands of years, it left behind layered deposits of lacustrine mudstone, conglomerate, volcanic ash, and shoreline tufa. These sediments now erode into the distinctive soft hills and ridges seen today.
The age of these deposits is constrained by air-fall volcanic ash layers (tephra) embedded within the sediments. These ash layers correlate with major eruptions in the western United States, including the Huckleberry Ridge Tuff from the Yellowstone caldera (about 2.02 million years ago), the Bishop Tuff from the Long Valley caldera (about 0.73 million years ago), and the Lava Creek Tuff from the Yellowstone caldera (about 0.62 million years ago).
Together, these deposits provide clear evidence of a wetter Mojave Desert past, when closed basins like Tecopa held standing water for extended periods. The Tecopa Mud Hills remain one of the most accessible and visually distinct records of that ancient lake system.
Ma. = million years ago
Source: Late Tertiary and Quaternary Geology of the Tecopa Basin, Southeastern California, by John W. Hillhouse