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.^[2]

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Hall Lake Formation
Stratigraphic range: Late Cretaceous, Campanian–Maastrichtian ~83.5–66.0 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Type	Geological formation
Unit of	McRae Group
Underlies	Jose Creek Member[1]
Overlies	"Quaternary-Tertiary basalt flows and alluvium"
Lithology
Primary	Mudstone, "shale", sandstone
Location
Coordinates	33.2°N 107.1°W / 33.2; -107.1
Approximate paleocoordinates	40.5°N 81.1°W / 40.5; -81.1
Region	New Mexico
Country	United States
Hall Lake Formation (the United States) Show map of the United States Hall Lake Formation (New Mexico) Show map of New Mexico

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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,^[3] 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,^[4] others classify it as a distinct formation in a group of formations.^[5]