The Hall Lake Formation in Sierra County, New Mexico, is a fossil-bearing geologic unit known for preserving Lancian fauna, including dinosaur remains. Geologists have also called it the Hall Lake Member, reflecting differing interpretations of its place in the local rock sequence. Regarded as part of the McRae Group and associated with the Elephant Butte and Staton-LaPoint locales, it overlies the Jose Creek Member and consists of purple and maroon shales, with its base marked by either a conglomerate or a color change. Its fossils, including Compsemys, support a Campanian-Maastrichtian age, while nearby basalt flows and alluvium show the region records a much longer geologic history.