The Summerville Formation is a Late Jurassic rock unit spread across parts of Utah, Colorado, and New Mexico in the Four Corners region and southwestern Colorado Plateau. Composed mainly of red mudstone with thin sandstone beds, it records a dry, low-relief coastal plain or sabkha that developed as the Sundance Sea retreated northward. Features such as desiccation cracks, gypsum, salt-hopper casts, and windblown sand point to saline lakes and drought-prone conditions. Though fossils are scarce, theropod tracks preserve brief signs of dinosaur activity. First defined in 1928, the formation remains important for reconstructing Jurassic environments in the interior West.