The Redonda Formation in eastern New Mexico preserves an important record of a late Triassic lake basin and the life that inhabited it. Composed of interbedded fine-grained red-brown sandstone and mudstone, it sits above the Bull Canyon Formation and below the Entrada Formation in the local sequence. Geologists interpret its sediments as deposits from a lake covering about 5,000 square kilometres. Though fossil plants are rare, the formation has produced abundant invertebrates, diverse vertebrates, and notable theropod tracks. First named in 1947 and elevated to formation rank in 1959, it remains a significant Triassic unit for both stratigraphy and fossils.