# Hall Lake Formation

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.

## Fossil content
### Dinosaurs
#### Saurischians

| Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon | Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited. |
| Genus | Species | Locality | Material | Notes |
| Tyrannosauridae | indet. | Staton-LaPoint | TKM001, dorsal vertebral centrum | Lozinsky et al. (1984) call it indeterminate |
| Tyrannosaurus | T. mcraeensis | Elephant Butte (upper) | NMMNH P-3698, a partial skull, lower jaw bones, teeth, and chevrons | |
| Alamosaurus | sp. | upper | TKM007, a damaged humerus | Tentative referral |
| Sauropoda | | | | Possibly from the Jose Creek Member |
| Theropoda | | | | Possibly from the Jose Creek Member |

#### Ornithischians

| Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon | Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited. |
| Taxon | Locality | Material | Notes |
| Triceratops sp. | 2 miles south of Elephant Butte | USNM 243, dorsal vertebral centrum | This genus, Torosaurus or a novel taxon |
| Sierraceratops turneri | Elephant Butte (lower) | Partial skeleton with skull | |
| Ceratopsidae | Elephant Butte (upper) | TKM002, a coranoid TKM020, crest fragment | A new genus similar to Torosaurus is said to exist above the base of the formation |
| Ceratopsidae | Elephant Butte (lower) | TKM002, a coranoid TKM020, crest fragment | Indeterminate, in abundance |
| Torosaurus sp. | Elephant Butte (upper)? | | |
| Hadrosauridae | cannot be determined | | Indeterminate and of unknown origins due to faulting or Quaternary cover |
| Ankylosauria | | TKM011, pyramidal bone fragment | Possibly from the Jose Creek Member, near identical from UNM-FKK-001P of the Kirtland Formation |

### Reptiles

| Taxon | Locality | Notes |
| Testudinata | Elephant Butte (upper) | |
| Crocodylia | Elephant Butte (upper) | |
| Compsemys | | Index fossils suggesting a Lancian age |
| Bothremydidae | | Index fossils suggesting a Lancian age |

### Plants

| Genus | Species | Locality | Material | Notes |
| Araucarites | A. sp. | | | |
| Cinnamomum | C. sp. | | | |
| Exnelumbites | E. morphotype 2 | | Leaves | A member of Nelumbonaceae |
| Ficus | F. sp. | | | |
| Phyllites | P. sp. | | | |
| Sabal | S. sp. | | | |
| Sabalites | S. sp. | | | |
| Salix | S. sp. | | | |
| Sequoia | S. sp. | | | |
| Tracheophyta | Indeterminate | 2 miles south of Elephant Butte | | |
| Viburnum | V. sp. | | | |