The Hall Lake Formation, formerly called the Hall Lake Member, is a geological formation in Sierra County, New Mexico preserving Lancian fauna, most notably dinosaurs. It is regarded as a member of the McRae Group, including the Elephant Butte and Staton-LaPoint locales.
Description
While most estimates place it firmly within the Lancian fauna, specifically using taxa such as Compsemys as index fossils to recover a Campanian-Maastrichtian age, Lozinsky et al. (1984) note the presence of basalt flows and alluvium dating to the Quaternary-Tertiary.
It overlooks the Jose Creek Member and is composed of purple and maroon shales. When they meet, it is marked by a basal conglomerate or a color distinction where conglomerate is absent. Various Cenozoic units overly the formation. Where some choose to classify these layers as a member of the McRae Formation, others classify it as a distinct formation in a group of formations.